All articles starting with R
22,461 articles
Referendums related to the European Union
Referendums related to the European Union: national votes on EU membership, treaty ratification, and policy opt-outs. 58 held by 2022; key cases include the 2005 French and Dutch rejections, Brexit 2016, and Iceland 2026.
Referential integrity
Referential integrity is a database property requiring that every foreign key value matches a referenced key or is null, enforced in SQL by foreign key constraints.
Referential thinking
Referential thinking, also called ideas of reference, is the tendency to interpret neutral events or others' actions as carrying unusual meaning directed at oneself; it is a common psychotic symptom.
Referential transparency
Referential transparency is the property of an expression that it can be replaced by an equal-valued expression without changing the enclosing expression's behavior, a term from Quine adopted into computer science by Strachey.
Referred pain
Referred pain, also called pain referral, is pain felt at a site distant from its source, such as cardiac pain in the left arm or gallbladder pain in the right scapula, explained mainly by convergence projection.
Refill friction stir spot welding
Refill friction stir spot welding, also known as friction spot welding, is a solid-state welding process that joins overlapping light-metal sheets without leaving a keyhole.
Refinancing
Refinancing is the replacement of an existing loan with a new one on the same asset and borrower, typically to lower the rate or take cash out.
RefinedWeb
RefinedWeb is a five-trillion-token English pretraining dataset built by the Technology Innovation Institute from filtered Common Crawl and announced in June 2023, serving as the data foundation of the Falcon language models.
Refinement type
A refinement type is a data type paired with a logical predicate restricting which values it admits, so a static checker can verify program properties at compile time.
Refinitiv
Refinitiv was a London-based financial markets data and infrastructure company created in 2018 when Blackstone bought a stake in Thomson Reuters' Financial & Risk business; LSEG acquired it in 2021.
Reflation
Reflation is the deliberate use of fiscal, monetary, or exchange-rate policy to lift an economy out of a downturn by raising spending, output, and the price level after deflation.
Reflect Orbital
Reflect Orbital is an American aerospace startup, founded in 2021 and based in the Los Angeles area, that plans to sell "sunlight on demand" by reflecting sunlight from satellites onto the ground at night.
Reflectance spectroscopy
Reflectance spectroscopy, also called IR reflectance spectroscopy, measures light reflected from a material's surface as a function of wavelength, yielding film thickness, roughness, and optical constants for applications from thin-film metrology to remote sensing.
Reflectarray antenna
A reflectarray antenna is a high-gain antenna whose flat surface of hundreds of phased elements reflects a feed's signal into a collimated beam, first demonstrated in 1963.
Reflected Brownian motion
Reflected Brownian motion, also called regulated Brownian motion, is a Markov process behaving like Brownian motion in a domain but pushed back at its boundary.
Reflected ceiling plan
A reflected ceiling plan (RCP) is a two-dimensional construction drawing showing everything on a ceiling, drawn as if reflected in a mirror on the floor so it aligns with the floor plan.
Reflecting telescope
A reflecting telescope, or reflector, uses a curved mirror instead of a lens to focus light; Isaac Newton built the first successful one in 1668.
Reflection (Fifth Harmony album)
Reflection is the 2015 debut studio album by American girl group Fifth Harmony (Epic/Syco), featuring "BO$$", "Sledgehammer", and "Worth It"; RIAA Gold then Platinum, Canada Gold, 2.3 billion Spotify streams.
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface so that part or all of the wave returns into the medium it came from.
Reflection (song)
"Reflection" is a 1998 ballad by Matthew Wilder and David Zippel from Disney's animated Mulan, sung in the film by Lea Salonga (2:27) and as a pop end-credits single by 17-year-old Christina Aguilera, her debut single, with Mandarin (Coco Lee), Spanish, and 2020 re-recorded versions.
Reflection AI
Reflection AI is an American artificial intelligence startup founded in 2024 in Brooklyn, New York, by former Google DeepMind researchers Misha Laskin and Ioannis Antonoglou.
Reflection coefficient
The reflection coefficient, also called the coefficient of reflection, is the fraction of a wave's amplitude reflected at a boundary, used in transmission lines, acoustics, and optics.
Reflection equation algebra
A reflection equation algebra is a quadratic associative algebra built from matrix solutions of the reflection equation, which describes particle scattering from a boundary in integrable systems.
Reflection Grating Spectrometer
The Reflection Grating Spectrometer (RGS) is a pair of X-ray spectrometers aboard ESA's XMM-Newton observatory, the first to use reflection gratings, covering the 0.33 to 2.5 keV band.
Reflection high-energy electron diffraction
Reflection high-energy electron diffraction (RHEED) is a surface analysis technique in which grazing-angle high-energy electrons reveal the top atomic layers, used to monitor epitaxial thin-film growth in molecular beam epitaxy.
Reflection in a Dead Diamond
Reflection in a Dead Diamond (Reflet dans un diamant mort) is a 2025 Eurospy homage thriller by Hélène Cattet and Bruno Forzani, their fourth feature, about a retired spy's blurring 1960s memories; it premiered at Berlinale 2025.
Reflection interference contrast microscopy
Reflection interference contrast microscopy (RICM), or interference reflection microscopy, is a label-free optical technique measuring nanometer-scale distances between a cell membrane and a transparent surface, widely used to study cell adhesion.
Reflection nebula
A reflection nebula is a cloud of interstellar gas and dust that produces no light of its own but scatters starlight from nearby stars, usually appearing blue.
Reflection principle
A reflection principle in set theory states that any first-order statement true of the universe of sets V is already true in some smaller set-sized Vα.
Reflection principles
A reflection principle is a formal schema asserting that a theory is sound, meaning every sentence it proves is true; it extends theories beyond what they can prove about themselves.