R

R is the eighteenth letter of the Latin alphabet. It may also refer to:

Mathematics

• The set of all real numbers, often written as or R
• The Pearson product-moment correlation coefficient r in statistics

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

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
• An electronic resistor, e.g. in circuit diagrams
• The R-# refrigerant numbering system

Physics, chemistry and biology

• A stellar classification, for orangish or K carbon stars
• R (cross section ratio), the ratio of hadronic to muonic cross sections
• Röntgen, a unit of measurement for ionizing radiation (such as X-ray and gamma rays)
• The Rydberg constant, a physical constant relating to energy levels of electrons within atoms
• The gas constant in chemistry
• In a chemical formula or structural formula, an unspecified group of atoms (denoting multiple possibilities exist)
• Arginine, an amino acid
• Relatedness, in biology
• Haplogroup R (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
• Haplogroup R (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
• ATC code R Respiratory system, a section of the Anatomical Therapeutic Chemical Classification System

Other uses

• R. (album) (1998) by R. Kelly
• A film rating in the Motion Picture Association of America film rating system
• Rated R (Queens of the Stone Age album), an album by "Queens of the Stone Age"
• R Cable, a Galician Telecommunications Company
• Rolled-R, the alveolar trill of Spanish, Italian, & Arabic languages
• The three Rs of Reading, wRiting and aRithmetic
• In The World Is Not Enough, a character played by John Cleese
• R·Type, an arcade video game
• ®, the symbol marking a registered trademark
• The Rand (currency) of South Africa
• Japan Radio Company's mobile phone of NTT DoCoMo in Japan
• Ryder's NYSE ticker symbol
• R (New York City Subway service)

This disambiguation page lists articles associated with the same Latin letter. If an internal link led you here, you may wish to change the link to point directly to the intended article.