A more thorough explanation:

Definition: A prisoner at the bar is an old-fashioned term used to describe a person who is on trial and accused of a crime.

Example: The prisoner at the bar was charged with theft and was awaiting his sentence.

Explanation: The example illustrates the definition by showing how the term "prisoner at the bar" is used to describe a person who is on trial and accused of a crime. The accused person is standing at the bar of the court, waiting for the judge to deliver their verdict.