A more thorough explanation:

Informal marriage, also known as common-law marriage, is a type of marriage that is recognized in some states when two people live together as husband and wife, intend to be married, and hold themselves out to others as a married couple without obtaining a marriage license or having a formal ceremony. This type of marriage is equivalent to a ceremonial marriage and can only be dissolved by annulment, divorce, or death.

For example, in Texas, a couple can establish an informal marriage by signing a declaration of informal marriage or by meeting certain requirements, such as living together for a certain period of time and presenting themselves as married to others.