At the discretion of of the performer as to tempo, expression, and so forth; an instrumental part that may be omitted
ad lib: A term which permits the performer to vary the tempo and/or to include or omit a vocal or instrumental part Synonymous with a piacere
ad lib - A term which permits the performer to vary the tempo and/or to include or omit a vocal or instrumental part Synonymous with a piacere
"At pleasure " Generally abbreviated ad lib According to the context the performer has the freedom to 1) interpret a passage as he wishes, without regard for strict time, 2) to make use of an alternate notes or notes provided by the composer, or 3) to improvise