Annulment is a very unusual remedy.
With the exception of bigamy and not meeting the minimum age requirement for marriage, it is rarely granted. A marriage can be declared null and void if certain legal requirements were not met at the time of the marriage. If these legal requirements were not met then the marriage is considered to have never existed in the eyes of the law. This process is called annulment. It is very different from divorce in that while a divorce dissolves a marriage that has existed, a marriage that is annulled never existed at all.