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.
More at: Annulment
More at: annulment