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R (disambiguation)

Last updated May 05, 2025

R , or r, is the eighteenth letter of the English alphabet.

Science

Biology and medicine

Arginine, an amino acid abbreviated as Arg or R
ATC code R Respiratory system, a section of the Anatomical Therapeutic Chemical Classification System
Coefficient of relationship (r), in biology
Effective reproduction number (R), the number of cases generated by one case in the current state of a population in epidemiology
- Basic reproduction number (R₀), the expected number of cases directly generated by one case
Haplogroup R (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
Haplogroup R (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
Net reproduction rate (R₀), the average number of offspring that would be born to a female given conforming conditions
r, the population growth rate in the r/K selection theory of ecology

Astronomy

Spectral resolution ( $\mathbb {R}$ ), in astronomy
Orangish or K carbon stars (stellar classification: R)

Physics

R (cross section ratio), the ratio of hadronic to muonic cross sections
Electrical resistance (R)
Roentgen (unit) (R), a unit of measurement for ionizing radiation such as X-ray and gamma rays
Rydberg constant (R_∞, R_H), a physical constant relating to energy levels of electrons within atoms
- Rydberg unit of energy (R_y), the energy of the photon whose wavenumber is the Rydberg constant

Temperature scales

Rankine scale (°R, °Ra)
Réaumur scale (°Ré, °Re, °r)
Rømer scale (°R, °Rø)

Chemistry

Gas constant (R), in chemistry
R, one of two chiral center configurations in the R/S system
Alkyl group, commonly marked as R in structural formulas
Side chain (an unspecified group of atoms), in a chemical or structural formula

Mathematics

r is the symbol for the radius of a circle
$\mathbb {R}$ or R, the set of all real numbers
Pearson product-moment correlation coefficient (r), in statistics
R (programming language), an environment for statistical computing and graphics
Ricci curvature
$Γ$ , the gamma function

Technology and engineering

R-value (insulation), a non-SI measure of thermal resistance used in housing insulation
R-value (soils), property of soils used in pavement design
Resistor, an electronic component
R-, a refrigerant numbering system
R, the ratio between the minimum and maximum stresses in fracture mechanics
R- or recall-button, now mostly used to switch between two calls

Computing

R (programming language), an environment for statistical computing and graphics
R (complexity), the set of all recursive languages
IBM System R, an IBM database system
RequestBot, a service in QuakeNet's IRC services

Arts and entertainment

Music

Ritardando, a term for slowing the tempo down gradually
R. (R. Kelly album), a 1998 album by R. Kelly
R° (Ruratia album), a 2002 album by Rurutia
R (single album), a 2021 single album by Rosé
Rated R (Queens of the Stone Age album), 2000 album also called R
R (jp), 2005 J-Pop album by Ryoko Shiraishi

Film

R (film), a 2010 film by Danish screenwriter and film director Tobias Lindholm
R, a character played by John Cleese in The World Is Not Enough
R, the protagonist of Warm Bodies, based on the book of the same name
R, a film rating in the Motion Picture Association of America film rating system and in the Canadian Home Video Rating System

Television

Rajawali Televisi (RTV), television in Indonesia
R, the production code for the 1965 Doctor Who serial The Chase

Video games

R·Type , an arcade video game
R: Rock'n Riders, in the list of PlayStation games (M–Z)

Organisations

The Crown, Rex (King) or Regina (Queen) in Commonwealth nations
Ryder (NYSE ticker symbol)
R (cable operator), a telecommunications company
R, denoting a member of the US Republican Party

Transportation

Nissan Skyline GT-R, commonly referred to as the "R" among Japanese speakers
R (New York City Subway service)
Rinkai Line, a railway line operated by the Tokyo Waterfront Area Rapid Transit, labeled R
Transilien Line R, a line of the Paris transport network
Reconnaissance aircraft (military designation: R)
Restricted airspace
Volkswagen R, the performance division of Volkswagen
The official West Japan Railway Company service symbol for:
- Hanwa Line.
- San'yō Main Line.

Other uses

Registered trademark symbol (®)
South African rand (R), a currency
Right (direction)
Rolled R (IPA: r), the alveolar trill of Spanish, Italian, & Arabic languages
ʀ, symbol for transliteration of the Younger Futhark rune ᛦ
ʀ, the voiced uvular trill
UTC−05:00 (military time zone code: Romeo)
Я, a Cyrillic letter similar to R
Subreddit, user-created areas of interest where discussions on Reddit are organized.

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R (disambiguation)

Contents

Science

Biology and medicine

Astronomy

Physics

Temperature scales

Chemistry

Mathematics

Technology and engineering

Computing

Arts and entertainment

Music

Film

Television

Video games

Organisations

Transportation

Other uses

See also