BC

BC, meaning Before Christ, was an initialism used to designate an Earth year's position relative to year zero. Hence, 1 BC was 1 year before 0. The term "BC" thus designated a negative number; 100 BC was 99 years before 1 BC. Its positive counterpart was AD.

Behind the scenes

An inherently Christian designation, BC is not generally used in calendars of the traditionally non-Christian world. Consequently, some people use BCE (meaning Before Common Era) for BC and CE (meaning Common Era) for AD. This is thought to avoid religious offense. However, Doctor Who fiction has typically remained loyal to the BC/AD convention. Even as late as the Steven Moffat era, dialogue and on-screen graphics prefer the Christian convention. (DW: The Fires of Pompeii, The Pandorica Opens, A Good Man Goes to War)