A more thorough explanation:

Definition: Espousals are mutual promises made between a man and a woman to marry each other.

For example, if John promises Mary that he will marry her in the future, and Mary promises John the same, they have made espousals per verba de futuro. On the other hand, if John and Mary declare that they are husband and wife at that very moment, they have made espousals per verba de praesenti.

These promises are legally binding and can be enforced in court if one party breaches the agreement.