R (disambiguation)
R is the eighteenth letter of the Latin alphabet.
R or r may also refer to:
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 (), 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∞, RH), a physical constant relating to energy levels of electrons within atoms
- Rydberg unit of energy (Ry), 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
- or R, the set of all real numbers
- Pearson product-moment correlation coefficient (r), in statistics
- Ricci curvature
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 in Japan
- 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:
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
- UTC−05:00 (military time zone code: Romeo)
- Я, a Cyrillic letter similar to R
See also
- R. (disambiguation)
- "R" Is for Ricochet, the eighteenth novel in Sue Grafton's "Alphabet mystery" series, published in 2004
- The three Rs, of reading, writing and arithmetic
- RR (disambiguation)
- RRR (disambiguation)
- RRRR (disambiguation)
- R class (disambiguation)
- Model R (disambiguation)
- Type R (disambiguation)
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