A.D = Anno Domini Latin for "year of our lord"
B.C.E = Before the Common Era
C.E = Common Era this is a synonym for A.D
I remember learning B.C and B.C.E mean the same although B.C.E is used more in Science to show respect spiritually. If a person is refering to Science they will most likely say B.C.E instead of B.C
...hope this helps.