Glossary R - Yenra

36 definitions in this view. Search all 509 terms by name, phrase or topic.

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A quantity derived from radar echoes that describes scattering by targets. Weather-radar reflectivity is commonly displayed on the logarithmic dBZ scale. Particle size, type and concentration, as well as unwanted echoes, affect the result. Interpret it with other observations when estimating precipitation; Doppler velocity measures a different property, motion along the viewing direction.

Guide: NASA's NPOL Radar: How Scientists Measure Rain and Snow

Reference: National Weather Service: dBZ and reflectivity interpretation

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Security & privacyRADIUS

Remote Authentication Dial-In User Service: a protocol used by network access equipment to consult a server about authentication, authorization and connection settings. Enterprise Wi-Fi commonly uses it between an access point or controller and a backend service. An Access-Accept response records one successful stage; address assignment and access to the intended application must also work.

Guide: Wireless LAN Authentication: 802.1X, RADIUS and EAP Methods

Reference: RFC 2865: RADIUS access requests and responses

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Computers & specificationsRAID

Redundant array of independent disks: a way of organizing multiple drives into one storage array. The chosen layout uses striping, mirroring or parity to balance capacity, performance and tolerance of drive failure; RAID 0 provides no redundancy. Keep a separate recovery plan for deletion, corruption or loss of the whole array.

Guide: RAID Levels Explained: Capacity, Drive Failures, and Recovery

Reference: Linux MD documentation: RAID layouts and failure behavior

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Computers & specificationsRAM

Random-access memory: the working memory a computer uses for active programs and data. Ordinary system RAM is volatile, so saving work to persistent storage serves a different purpose from adding memory capacity.

Read the guide: Technology Terms That Help You Read Product Specifications

Reference: Kingston: memory and storage

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Transport & aerospaceRamjet

An air-breathing jet engine that uses forward motion to compress incoming air before combustion. It requires incoming airflow at suitable speed rather than a conventional rotating compressor.

Reference: NASA: ramjet and scramjet propulsion

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Science & measurementRandomization (experiments)

Using a chance-based procedure to assign experimental units to conditions or determine run order. This helps prevent treatment conditions from systematically aligning with other influences, such as measurement order. Random assignment supports a fair comparison within the experiment; representative population sampling addresses the separate question of whom or what the results describe.

Guide: Research Design Tools: Turn a Question into a Testable Experiment

Reference: NIST: completely randomized designs

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Security & privacyRansomware

Malware or an attack that blocks access to data or systems, often through encryption, while demanding payment. Attacks can also involve stolen data; recovery planning needs to address both system restoration and exposure.

Read the guide: Anti Virus and Malware: Protection, Recovery, and Outbreak Lessons

Reference: CISA: ransomware guide

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PhotographyRAW image file

A camera file containing sensor-derived image data and metadata for later processing. Formats and software support vary; retaining the original file and its editing information allows future reinterpretation of the photograph.

Read the guide: Photo Storage: Organize, Back Up and Recover Your Pictures

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AccessibilityReading order

The sequence in which content is presented for reading, including through assistive technology. In a PDF, structure tags help determine this sequence. A two-column page should read in a meaningful order instead of jumping between unrelated lines. Check reading order and the tab sequence through interactive controls as separate tasks.

Guide: Accessible PDFs with Adobe Acrobat: Create, Check and Repair

Reference: W3C: PDF reading and tab order

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Security & privacyRecovery key (device encryption)

Recovery material used to unlock encrypted storage when its usual unlocking method is unavailable. BitLocker, for example, uses a 48-digit recovery key that may be requested after a hardware or security change. Confirm access to the correct recovery material before replacing a drive, and keep it secure separately from that drive.

Guide: Toshiba XG5-P Client NVMe SSD: Compatibility and Upgrade Checks

Reference: Microsoft: finding a BitLocker recovery key

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Science & measurementRedshift

A shift of a spectral feature toward longer wavelengths compared with its known emitted wavelength. Redshift z equals observed wavelength divided by emitted wavelength, minus one. Cosmological redshift reflects the expansion of space during light's journey; motion and gravity can also shift light. Inferring cosmic distance or lookback time requires an appropriate model.

Guide: The Most Distant Galaxies: Redshift, Lookback Time and Confirmation

Reference: NASA Hubble: interpreting cosmological redshift

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Food & cookingReduction (cooking)

Cooking a liquid so some evaporates, leaving a smaller, more concentrated amount. A reduced stock or sauce can gain stronger flavor and a thicker consistency, depending on what remains in it. Reduction removes liquid; it is different from thickening by adding starch. Taste again afterward because salt and other retained ingredients have also become more concentrated.

Guide: Culinary Vinegar: Choose a Type and Balance a Dish

Reference: Professional Cooking: sauce reduction, chapter 9 (PDF)

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AccessibilityReflow (content)

The rearrangement of content to fit the available viewing space as a window narrows or text is enlarged. Paragraphs wrap and sections can stack while retaining their meaning and usable controls. This lets readers follow ordinary text without scrolling sideways for each line; maps and some other two-dimensional content need separate treatment.

Guide: Website Accessibility Check: A Practical First Audit

Reference: W3C: Reflow

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Audio & videoRefresh rate

The frequency at which a display refreshes its image, measured in hertz (Hz). A 60 Hz mode refreshes 60 times per second. Compare this with the content's frame rate: a high refresh-rate display still needs suitable frames, settings and a supported connection to deliver the intended motion experience.

Guide: Choosing a Graphics Card: Workloads, VRAM, Power, and Fit

Reference: Microsoft: display refresh rate

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Computers & specificationsRegression testing

Software testing after a change to check whether behavior that previously worked has been unintentionally affected. Relevant checks can be automated or manual and should cover meaningful user outcomes. After repairing a form label, for example, check that repeated fields still have distinct usable names and that the form’s other essential interactions continue to work.

Guide: Accessibility Evaluation and Repair: From Finding to Retest

Reference: ISTQB: selecting regression tests after changes (PDF)

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Rocks & EarthRelative sea level

Sea-surface height measured relative to a local land reference. Changes reflect both the water level and vertical movement of the land: sinking land can increase local relative rise, while uplift can reduce it. A tide-gauge trend describes an observed location and period; future planning also requires suitable scenarios and their assumptions.

Guide: Sea Level Rising: Read Local Trends and Future Scenarios

Reference: NOAA: relative sea level and land motion

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Science & measurementRepeatability (measurement)

Closeness of repeated measurement results under specified repeatability conditions: the same procedure, operator, measuring system, operating conditions and location over a short period. A small spread indicates good repeatability for those conditions. Consistently biased readings can still cluster tightly, so repeatability and agreement with a reference value require separate checks.

Guide: Pipetting: Improve Accuracy, Precision, and Repeatability

Reference: JCGM VIM: measurement repeatability · JCGM VIM: repeatability conditions

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Computers & specificationsReplication (storage)

Maintaining another copy of stored data by copying changes to a second location or system. Synchronous replication waits for the destination to acknowledge a write; asynchronous replication can leave the destination behind the source. Replicated deletions or corruption can affect both copies, so plan retained recovery versions and independent backups alongside replication.

Guide: Storage Mirroring and Replication: Failure Scenarios and Recovery Tests

Reference: Microsoft: synchronous and asynchronous storage replication

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Computers & specificationsRestore (data)

Returning files or a system from a saved backup to a usable location or state. A restore may recover one document, an earlier version or an entire system, depending on the backup. Opening recovered files and checking required applications tests whether the saved copy meets the recovery need.

Guide: Toshiba XG5-P Client NVMe SSD: Compatibility and Upgrade Checks

Reference: Microsoft: backup, restore and recovery

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Science & measurementRetention time (chromatography)

The elapsed time between sample injection and the position of a component's peak in a chromatogram, commonly measured at the peak maximum. It depends on the separation method and operating conditions. Comparing retention times with suitable standards can support identification, while overlapping or coeluting components require additional evidence.

Guide: Mass Spectrometry: Read the Signal and Understand the Evidence

Reference: Shimadzu: retention-time parameters

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NetworksRFID

Radio-frequency identification: using radio communication between a reader and a tag to identify or obtain information about an item. Tag type, frequency, placement and surroundings affect the read.

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Energy & environmentRFS

Renewable Fuel Standard, a U.S. program governing renewable-fuel obligations in transportation fuel. Requirements depend on the applicable year and rules; use EPA's current program information for those details.

Reference: EPA: Renewable Fuel Standard

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NetworksRNC

Radio network controller: equipment or a network function managing radio-access resources in certain cellular architectures. Its responsibilities depend on the network technology and generation.

Related coverage: EV-DO Rev A release 8

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PhotographyRolling shutter

A readout method that records different image rows at slightly different times. Fast subject or camera motion can therefore appear skewed, bent or banded; readout speed and lighting conditions affect the artifact.

Read the guide: CMOS Image Sensors: Size, Pixels, Noise and Shutter Readout

Reference: Sony: rolling shutter

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NetworksRoute processor

A router component that performs control functions such as maintaining routing information. How control and forwarding are divided depends on the router's architecture.

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NetworksRouter

A device or software function that forwards packets between networks using forwarding information. Its interface support and configuration determine which networks it connects.

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Computers & specificationsRPO

Recovery point objective: the maximum acceptable period of data loss after an outage, expressed as time. A five-minute RPO means planning to recover data no more than five minutes behind the disruption. Measure the latest usable recovered data to check the objective; backup frequency alone does not establish the achieved result.

Guide: Storage Mirroring and Replication: Failure Scenarios and Recovery Tests

Reference: Microsoft: recovery point and recovery time objectives

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Historical names & systemsRPP

Rapid prototyping platform, a term used in the linked prototyping-equipment coverage. Identify the actual manufacturing process and machine when interpreting a platform's claimed capabilities.

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Computers & specificationsRS-232

A standard family for serial communication interfaces, including electrical signaling between equipment. RS-232 signaling differs from the low-voltage logic used by many microcontroller UART pins, so an appropriate interface circuit may be required. Verify voltage levels, connector pinout, transmit/receive roles and handshake wiring from both devices’ documentation before connecting them.

Guide: Bluetooth Serial Adapters: Compatibility, Setup, and Testing

Reference: Texas Instruments: translating RS-232 and logic-level signals

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NetworksRSSI

Received Signal Strength Indicator: a receiver’s reported indication of the strength of a received radio signal. Many tools express it in dBm, while reporting scales and measurement details depend on the technology and implementation. Compare readings under consistent conditions alongside noise, packet delivery and application performance; signal strength alone gives an incomplete picture of link quality.

Guide: Bluetooth Transceivers: Radio Range, Antennas, and Link Budgets

Reference: Silicon Labs: a Bluetooth RSSI measurement and its units

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Science & measurementRSS (solar measurement)

Rotating shadowband spectroradiometer: an instrument that uses a moving shadowband and spectral measurements to study sunlight components. Its calibration and measurement geometry matter to the resulting data.

Reference: ARM: rotating shadowband spectroradiometer (PDF)

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Web & documentsRSS (web feeds)

Really Simple Syndication, also associated with the name Rich Site Summary: a family of web-feed formats for distributing updates. A feed reader can follow newly published items without visiting each page individually.

Related coverage: Web Feeds

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Transport & aerospaceRTK

Real-time kinematic positioning: a GNSS method that combines satellite carrier-phase measurements with timely reference-station or network correction data. It can support very precise positioning when the receiver resolves the carrier ambiguities and conditions are suitable. Check solution status, correction availability, antenna setup and surroundings before relying on a reported position.

Guide: GPS Chipsets and GNSS Modules: Selection and Integration

Reference: u-blox: high-precision GNSS and RTK

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Computers & specificationsRTO

Recovery time objective: the maximum acceptable time for a defined service to be unavailable after a disruption. Specify what counts as working again, such as completing an application transaction, and measure recovery against that endpoint. RTO concerns downtime; RPO concerns how much recent data can be lost.

Guide: Storage Mirroring and Replication: Failure Scenarios and Recovery Tests

Reference: Microsoft: recovery point and recovery time objectives

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Computers & specificationsRTOS

Real-time operating system: an operating system designed to support tasks with defined timing requirements. Meeting a deadline depends on the whole configured system, including applications and hardware.

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Tools & workshopRunout

Variation in a rotating tool or surface relative to its intended axis of rotation. Radial runout is measured across the axis; axial runout is measured along it. A wobbling drill or poorly seated bit can contribute to an uneven hole. Runout is a geometric condition, distinct from placing an otherwise accurate hole in the wrong location.

Guide: Drill Bits: Match the Material, Hole and Drill

Reference: Mitutoyo: circular and total runout (PDF)

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A starting point for understanding

Each entry gives a concise meaning and, where useful, a distinction or practical example. Topic labels identify the context; the same acronym can have several meanings. Historical names remain useful when reading older coverage.

Follow the linked Yenra guides for fuller explanations and the reference links for supporting documentation. Health, technical and regulatory terms describe concepts; individual decisions depend on the applicable evidence, equipment and circumstances.

Collection updated October 13, 2026. Full glossary · AI Glossary