A more thorough explanation:

An impediment is something that gets in the way or stops something from happening. In the context of marriage, it refers to a fact or circumstance that can prevent a marriage from being valid or legal.

• Canonical impediment: This is a reason for annulment recognized by the Roman Catholic Church. Examples include affinity (being too closely related to someone), impotence (being unable to have sexual intercourse), disparity of worship (having different religious beliefs), and previous religious profession (being a member of a religious order).
• Civil impediment: This is a reason for annulment recognized by civil law. Examples include being a minor (underage), having unsoundness of mind (not being mentally capable of understanding the marriage), fraud (being deceived into the marriage), and duress (being forced into the marriage).
• Diriment impediment: This is a fact that makes a marriage void from the beginning. Examples include being too closely related to someone (consanguinity within a prohibited degree) and being already married (prior undissolved marriage).

These examples illustrate how an impediment can prevent a marriage from being valid or legal. For instance, if someone is already married, they cannot legally marry someone else until they have obtained a divorce or annulment. Similarly, if someone is underage, they cannot legally enter into a marriage contract.