A more thorough explanation:

Definition: Alibi is a defense used in criminal cases where the accused claims to have been somewhere else at the time the crime was committed.

Example: If someone is accused of robbing a bank at 2pm, but they can prove that they were at a doctor's appointment at that time, then they have an alibi.

Alibi can also be used as a verb when someone provides an alibi for another person.

Example: If a person claims that their friend was with them at the movies during the time of a crime, then they are providing an alibi for their friend.

These examples illustrate how alibi is used as a defense in criminal cases. If a person can prove that they were somewhere else at the time of the crime, then they cannot be guilty of committing the crime. Alibi can be an important tool in proving innocence in criminal cases.