The term "A.D." or
Anno Domini (the year of our Lord) is lately being replaced by terms attempting to de-Christianize the standard time measurement, with terms like B.C.E. (before common era), which comes with its own set of problems, in eliminating the source-point from which time is measured.
But even A.D. has its problems. Even after Wikipedia's explanation, it still leaves an ambiguity and potential gap in time measurement, in not giving a "zero" starting point.
There's a question of how one measures time. The starting point is the birth of Christ. "B.C." or Before Christ is fairly easy, it just measures backward from the point of Jesus' birth.
But "A.D." is a bit more difficult. Jesus lived for 33 years.
So does 1 A.D. measure 1 year after Jesus' birth?
Or is it 1 year after his death (which could alternately be 33 + 1, or 34 A.D.)?
i.e., one year after His birth, vs. 1 year after his death. Which potentially leaves a gap of time measurement of 33 years of Jesus' life excluded from time measurement, measuring only backward from Jesus' birth (B.C., Before Christ), and forward from the point of his death (A.D., After Death).
Even Wikipedia's long-winded explanation doesn't adequately clarify that.
