According to the earliest definition of the radiocarbon scale
we know of, and that was defined at the very first radiocarbon
conference in Andover, 1954, and which was cordially agreed on
by all attendants e.g. Hans Suess, and that was later never
cordially changed, the abbreviation "BP" means "Before Physics".
The following link shows that this (correct) definition is indeed
sometimes in use (note the download of 1.2 MB):
BP=Before Physics (AD 1950)