What is Marriage License?

Legal Definition
A marriage license is a document issued, either by a church or state authority, authorizing a couple to marry. The procedure for obtaining a license varies between countries and has changed over time. Marriage licenses began to be issued in the Middle Ages, to permit a marriage which would otherwise be illegal (for instance, if the necessary period of notice for the marriage had not been given).

Today, they are a legal requirement in some jurisdictions and may also serve as the record of the marriage itself, if signed by the couple and witnessed.

In other jurisdictions, a license is not required. In some jurisdictions, a "pardon" can be obtained for marrying without a license, and in some jurisdictions, common-law marriages and marriage by cohabitation and representation are also recognized. These do not require a marriage license. There are also some jurisdictions where marriage licenses do not exist at all and a marriage certificate is given to the couple after the marriage ceremony had taken place.

Article 16 of the Universal Declaration of Human Rights declares that "Men and women of full age, without any limitation due to race, nationality or religion, have the right to marry and to found a family. They are entitled to equal rights as to marriage, during marriage and at its dissolution. Marriage shall be entered into only with the free and full consent of the intending spouses."
-- Wikipedia
Legal Definition
A license or permission granted by public authority to persons who intend to intermarry. By statute in some jurisdictions, it is made an essential prerequisite to the lawful solemnization of the marriage.
-- Black's Law Dictionary
Legal Definition
A written license or permission granted by public authority to persons who intend to intermarry, usually addressed to the minister or magistrate who is to perfom the ceremony, or, in general terms, to any one authorized to solemnize marriages.
-- Black's Law Dictionary
Legal Definition
A license required in many states as a prerequisite to solemnization of the marriage.
-- Ballentine's Law Dictionary