In adaptive music, vertical composition, or reorchestration, is a technique in which a track continues to play throughout a section of a game, but as game parameters change, individual elements of the music track are added and removed.
For example, it is common in games to have a simple orchestral track that plays while the player explores an island, but with additional percussion that plays only when the player is in combat. The combat-triggered percussion is added in dynamically when the player enters combat, and is removed when combat is finished, all while the original track continues to play.
Compare to horizontal composition.