An annulment is a legal procedure undertaken by married individuals to denounce that their marriage as if never took place. The annulment process will declares a marriage null and void. An annulment is held in contrast to a divorce which recognizes that a marriage did in fact at one time take place. An annulment is therefore retroactive; an annulled marriage is considered to be invalid from the onset of the marriage.
A marriage is in essence a contract. Two individuals agree to the stipulations that the marriage enforces, and through this agreement, are connected in the eyes of the particular state government where the marriage took place. An annulment, as a result of its retroactive status, takes the contract and deems it void, which in turn rules the wedding as null.