BC stands for Before Christ. AD stands for Anno Domini "In the year of the Lord".
This assumes that Jesus Christ was born in the year, well there is no year zero, the years
jump from 1 B.C. to A.D. 1, so when was Jesus born?
It has been determined that Jesus Christ could not have been born
any later than 4 B.C. because King Herod was in power at the time
and according to secular records King Herod died in 4 B.C.
offers us what looks like a convincing piece of historical detail when he
tells us that Jesus was born at the time of the census of Quirinius, which took place
in A.D. 6. Thus we have Jesus born no later than 4 B.C., and at the same time
no earlier than A.D. 6. The gospels are littered with such inconsistencies—just further
evidence that Jesus never existed.
Thus new names have come into usage to replace B.C. and A.D.
B.C.E. or B.P.
Before the Common Era or Before the Present era (same as B.C.)
Common Era (same as A.D.)
A.D. is usually placed before a date, as in A.D. 43.
all other abbreviations, B.C., B.C.E., B.P., C.E., are usually placed after the date.