What is Void Marriage?

Legal Definition
A void marriage is a marriage which is unlawful or invalid under the laws of the jurisdiction where it is entered. A void marriage is "one that is void and invalid from its beginning. It is as though the marriage never existed and it requires no formality to terminate."

A marriage, however, which can be canceled at the option of one of the parties is merely voidable, meaning it is subject to cancellation if contested in court. A marriage that is entered into in good faith, but which is subsequently found to be void, may be recognized as a putative marriage and the spouses as putative spouses, with certain rights granted by statute or common law, notwithstanding that the marriage itself is void.
-- Wikipedia
Legal Definition
A marriage that was for some reason never valid from the start and cannot be made valid. Common reasons for a court to find a marriage void ab initio are that the marriage is incestuous, polygamous, or a same-sex marriage.

Compare with voidable marriage.
Legal Definition
the term given to marriage with no legal validity as it is prohibited by law.
Legal Definition
One which is good for no legal purpose. See 44 Am. Dec. 54, note.
-- Ballentine's Law Dictionary