R is the eighteenth letter of the Latin alphabet. It may also refer to: [edit] Mathematics [edit] Computing [edit] Engineering [edit] 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
[edit] Other uses | Latin letter disambiguation | | A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P • Q • R • S • T • U • V • W • X • Y • Z | |