A more thorough explanation:

Definition: A "black maria" is a slang term used to describe a locked van that is used by the police to transport prisoners to and from jail.

Example: When the police arrested the suspect, they put him in the back of the black maria and drove him to the station.

Explanation: The example illustrates how the term "black maria" is used to describe a specific type of vehicle used by law enforcement to transport prisoners. The term is often used in a negative context, as it is associated with the process of being arrested and taken to jail.