It's also referred to as "leitmotif."
This was used in opera-scores, and carries over to contemporary film soundtracks. A passage or melody is used to represent a certain character or situation, and is re-used throughout the orchestration whenever the composer wants to emphasize that character or evoke a previous scene.
The term can also be used outside of the musical realm, to refer to a recurring theme in a story, or even in life!
