I think that does stand for "Before Christ":
https://en.wikipedia.org/wiki/Anno_Domini
Anno Domini (AD) and before Christ (BC) qualify years in the Gregorian and Julian calendars, whose epoch is the traditional year of the conception or birth of Jesus. AD counts years since the epoch, BC the years before the epoch.
The modern terms are called Common Era:
Common Era (CE) and Before the Common Era (BCE) are conventions used in the Gregorian or Julian calendar to specify whether the year is before or after the epoch. They correspond exactly to Anno Domini (AD) and Before Christ (BC): "2026 CE" is the same year as "AD 2026", as are "400 BCE" and "400 BC". BCE/CE are used to avoid religious associations by not referring to Jesus as Dominus ('Lord').
Personally, I think we should pick the start of the Holocene as year 0