A more thorough explanation:

A diriment impediment is a fact that makes a marriage completely invalid. It is a legal barrier that prevents a marriage from being recognized as valid. This means that if a diriment impediment is present, the marriage is considered void and never existed in the eyes of the law.

Examples of diriment impediments include:

• Consanguinity within a prohibited degree: This means that the couple is too closely related to each other, such as siblings or parent and child.
• Prior undissolved marriage: If one or both parties are still legally married to someone else, they cannot enter into a new marriage.

These examples illustrate how a diriment impediment can completely nullify a marriage. If a couple is found to have a diriment impediment, their marriage is considered void from the beginning, and they are not legally recognized as married.