Technology and the built world

Relation extraction

Relation extraction is the natural language processing task of identifying semantic relationships between entities in text, outputting structured triples that feed knowledge graphs and question answering.

Relational algebra

Relational algebra is a procedural query language for the relational model of databases, introduced by IBM researcher Edgar F. Codd in his 1970 paper on relational data.

Relational database

A relational database stores data in tables of rows and columns and follows the relational model proposed by E. F. Codd in 1970, queried with SQL.

Relational model

The relational model, also called the relational data model, organizes database data into tables called relations, and was proposed by E. F. Codd at IBM in 1970.

RelationalAI

RelationalAI is an American software company, founded in 2017 and based in Berkeley, California, whose decision intelligence platform runs a relational knowledge graph inside Snowflake.

Relative Entropy Policy Search

Relative Entropy Policy Search (REPS) is a reinforcement learning algorithm introduced by Jan Peters and colleagues in 2010 that bounds the KL divergence between successive policies.

Relative navigation

Relative navigation is the determination of a spacecraft's position, velocity, and attitude relative to another vehicle rather than a ground reference, enabling autonomous rendezvous, docking, on-orbit servicing, and planetary landing.

Relative pose estimation

Relative pose estimation is a computer vision method that determines the rotation and translation direction of one camera relative to another from point correspondences between two images.

Relativistic Heavy Ion Collider

The Relativistic Heavy Ion Collider (RHIC) was a particle collider at Brookhaven National Laboratory in Upton, New York, operating from 2000 to 2026 and recreating the quark-gluon plasma.

Relaxation oscillator

A relaxation oscillator is an electronic oscillator producing non-sinusoidal waveforms such as square, triangular, and sawtooth waves by repeatedly charging and discharging a capacitor between two switching thresholds.

Relaxation test

A relaxation test is a mechanical test that holds a specimen at a fixed strain and measures how the stress needed to hold it decays over time.

Relaxor ferroelectric

A relaxor ferroelectric is a ferroelectric material with a broad, frequency-dependent permittivity maximum and only nanometer-scale polar order, discovered by G. A. Smolenskii in the late 1950s.

Relay

A relay is an electrically operated switch in which a small current through a coil moves an armature that opens or closes contacts in a separate load circuit.

Relay beamforming

Relay beamforming is a wireless technique in which multiple relay stations jointly weight and combine signals, acting like a phased antenna array aimed at the destination.

Relay coordination

Relay coordination is the process of choosing protective relay settings and time delays so devices trip in sequence during a fault, isolating the smallest part of the power system.

Release paper

Release paper, also called release liner, is paper coated with a thin silicone layer that carries adhesives for labels and tapes, peeling away cleanly at use.

Relevance feedback

Relevance feedback is an information retrieval technique in which a search system reformulates a user's query based on documents marked relevant or nonrelevant, introduced by Rocchio in 1971.

Relevance vector machine

The relevance vector machine (RVM) is a Bayesian kernel method for regression and classification introduced by Michael E. Tipping in 1999, typically far sparser than the support vector machine.

Reliability block diagram

A reliability block diagram is a graphical model of system success as blocks in series or parallel, used to compute system reliability from component reliabilities.

Reliability growth model

A reliability growth model is a mathematical model predicting how the reliability of a repairable system or software product improves as defects are found and fixed during testing.

Reliability of Wikipedia

The reliability of Wikipedia, also called the accuracy of Wikipedia, is how accurate its volunteer-edited content is, as measured by external audits like Nature's 2005 comparison with Britannica.

Reliability-centered maintenance

Reliability-centered maintenance (RCM) is a structured method for deciding which maintenance tasks an asset needs, developed in the airline industry in the 1960s and named in a 1978 report to the U.S. Department of Defense.

Reliability, availability, maintainability and safety

Reliability, availability, maintainability and safety (RAMS) is an engineering framework that treats the four characteristics together to demonstrate the dependability of technical systems, most prominently in railways through the EN 50126 standard.

Reliance BP Energy Limited

Reliance BP Energy Limited, legally Reliance BP Mobility Limited, is a joint venture of Reliance Industries and bp trading as Jio-bp, formed in 2019 to run fuel stations across India.

Reliance Communications

Reliance Communications, also called Reliance Infocomm or RCom, was an Indian telecom company controlled by Anil Ambani; launched in 2003, it collapsed under debt after Reliance Jio's 2016 entry.

Reliance Power

Reliance Power Limited is an Indian private-sector power company of the Anil Ambani-led Reliance Group, operating about 5,305 MW of coal, gas, solar, wind, and hydro projects.

Reliance, Inc.

Reliance, Inc. is an American metals service center company headquartered in Phoenix, Arizona, and the largest in North America; founded in 1939, it had 2025 net sales of $14.29 billion.

Reliant Regal

The Reliant Regal was a British three-wheeled economy car built by Reliant of Tamworth from 1953 to 1973, ending with the glassfibre Regal 3/25 and 3/30 that preceded the Robin.

Reliant Robin

The Reliant Robin is a British three-wheeled economy car built by the Reliant Motor Company in Tamworth from 1973 to 2002, Britain's best-known three-wheeler, sellable on a motorcycle license.