what is withdrawal bleeding

started looking through this group and I see a lot of posts about withdrawal bleeding. when does this happen after going off BC? I went off mine at the end of August and just started my period at cd29. is this just my normal period? it was only 1 day later than usual, but I did have slight spotting the 2 days before it started, so overall not Mich different then normal. did I just not have withdrawal bleeding or was this withdrawal bleeding. sorry if it's a dumb question...