Common-law marriage in the United States
In the United States, common-law marriage is a legally recognized form of irregular marriage. Formed without a license or ceremony, common-law marriage has three requirements: (1) the couple agree that they are married, (2) the couple lives together in an intimate relationship, and (3) the couple presents themselves to the public as a married couple.
Source: Wikipedia — Common-law marriage in the United States (CC BY-SA 4.0)