A more thorough explanation:

Definition: A marriage that is entered into in secret, without all the required formalities or by an unauthorized person. It can also refer to a marriage that is based solely on the agreement of the parties involved.

Example: In the 17th and 18th centuries, Fleet marriages were a type of clandestine marriage that took place in the Fleet prison in London. These marriages were performed by chaplains who had been imprisoned for debt and were not authorized to perform marriages. The couples would pay the chaplain to perform the ceremony, and the marriage would be considered valid even though it did not follow the proper legal procedures.

Explanation: This example illustrates how a clandestine marriage can be performed by an unauthorized person and without all the required formalities. The couples in Fleet marriages were willing to take the risk of having a secret marriage because they could not afford to follow the proper legal procedures or because they wanted to avoid the social stigma associated with certain types of marriages.