What is Annulment?

Legal Definition
Annulment is a legal procedure for declaring a marriage null and void. Unlike divorce, it is usually retroactive, meaning that an annulled marriage is considered to be invalid from the beginning almost as if it had never taken place (though some jurisdictions provide that the marriage is only void from the date of the annulment; for example, this is the case in section 12 of the Matrimonial Causes Act 1973 in England and Wales). In legal terminology, an annulment makes a void marriage or a voidable marriage null.
-- Wikipedia
Legal Definition
Is a legal procedure that declares a marriage is null from its inception. Unlike divorce, the effect of declaring a marriage void is retroactive, meaning that the marriage was void at the time it was entered into. An annulment is only granted with a showing of grounds, such as incest or insanity.
Legal Definition
When an event or judgment is treated as if it never happened.