Archaeologists use the term BP to mean "years Before the Present", which avoids the whole philosophical debate about AD and BC versus CE and BCE. The only trouble is, the Present, of course, changes every year. Since the BP designation was at least originally associated with radiocarbon dating, archaeologists chose the year 1950 as 'the present'. Radiocarbon dating was invented in the late 1940s, and, also, atmospheric nuclear testing was begun in the 1940s, which makes, at least the theory goes, radiocarbon dates after 1950 virtually useless, anyway.
Of course, that begs the question of what do you call the period between 1950 and the present year. After Present? After Radiocarbon? After Nuclear Testing? Ah well, we can always fall back on the Julian calendar.
See the entries on RCYBP and Radiocarbon Dating for further information about carbon 14 dating.
Other Common Calendar Designations
Sources
Taylor, Timothy 2008 Pehistory vs. Archaeology: Terms of Engagement. Journal of World Prehistory 2:11–18.
This glossary entry is part of the About.com Guide to Calendar Designations and the Dictionary of Archaeology.
