Like Divorce, Annulment terminates the marriage. However unlike divorce, an Annulment makes the marriage as if it never existed.
For example, if a party gets an Annulment, they were never married. If a party gets a divorce, they were married but are now divorced. In order to get an Annulment and erase any trace of your marriage, you must have a legal reason.
Legal reasons for Annulment include Fraud, Lack of Consent, Incest, Bigamy, Duress, Inability to Consummate the Marriage, a party is Under Age without parental consent, a party entered the marriage on a Dare, or the marriage is Prohibited by Law.