Ad libitum (/ædˈlɪbᵻtəm/) is Latin for "at one's pleasure"; it is often shortened to "ad lib" (as an adjective or adverb) or "ad-lib" (as a verb or noun). The roughly synonymous phrase a bene placito ("in accordance with [one's] good pleasure") is less common but, in its Italian form a piacere, entered the musical lingua franca (see below).
The phrase "at liberty" is often associated mnemonically (because of the alliteration of the lib- syllable), although it is not the translation (there is no cognation between libitum and liber). Libido is the etymologically closer cognate known in English.
As a direction in sheet music, ad libitum indicates that the performer or conductor has one of a variety of types of discretion with respect to a given passage:
Ad-Libs is an improvisational comedy troupe based in Dallas, Texas. Combining improvisation along with video segments, Ad-Libs was conceived by Phil Larsson in 1986. Ad-Libs performs weekly shows at its 200 seat downtown Dallas cabaret style theater (Ad-Libs Improvisational Comedy Theater) and tours across the country for corporate events and performing arts centers.