Complete Encyclopaedia of Music/A/Accompaniment ad libitum

Accompaniment ad libitum, or AD LIB. Accompaniment at pleasure. This phrase implies that the movement, or piece, at the head of which it is placed, may be performed with or without the accompaniment. It does not, however, mean that the performance will be as perfect without as with the accompaniment ; but that the accompaniment may be omitted without any material detriment to the intended effect.