It normally refers to a timescale called "Before Present" where Present is defined as = Jan 1, 1950. You see it a lot in radio- dating. GP has invented their ow

It normally refers to a timescale called "Before Present" where Present is defined as = Jan 1, 1950. You see it a lot in radio- dating. GP has invented their own dating system with the same name based around ~2021. Fun fact, there's no corresponding After Present system for dates after 1950. Instead you subtract negative years. E.g. 1957 AD = -7 BP.