BC (not comparable)
- Initialism of Before Christ.. Often written in small caps.
- The Han Dynasty ruled China from 206 BC to AD 220.
- The Chicago Manual of Style as well as most house styles require placing the AD before the number of the year and BC after, although in casual use either abbreviation can be found in either place.
- Some use BCE, for "Before the Common Era", which is more secular in nature, to avoid potential Christian bias.
- a.d., AD, A.D. (anno Domini, Anno Domini, in the year of our Lord); CE (Christian Era, Common Era, Current Era)
- (British Columbia): "B.C." is the customary abbreviation of British Columbia as used in case citations; see e.g. The Bluebook: A Uniform System of Citation, Nineteenth Edition (2010), "Geographical Terms: Australian states and Canadian provinces and territories", Table T10.2, page 438.
- birth control
- (chemistry) Initialism of benzalkonium chloride.
- (US, navy) battlecruiser, a type of warship.
- (computer science) Initialism of backward compatibility.