Ad libitum

Ad libitum

[ad lib-i-tuhm; Lat. ahd lib-i-toom]
Ad libitum is Latin for "at one's pleasure"; often shortened to 'Ad lib' (as an adjective or adverb), or 'ad-lib' (as a verb or noun). There is a less commonly used synonym, a bene placito.


In music, this instruction appears in sheet music to indicate that a part can be left out, such as an unnecessary accompaniment or that a passage is to be played in free time rather than in strict tempo. This kind of freedom with the beat for expressive ends, when not explicitly indicated by the composer, is known in classical music as rubato. The expression repeat ad libitum means that a passage may be repeated an arbitrary number of times.

More generally, the phrase ad libitum can be used to indicate an improvisation.


Ad libitum is also used in psychology and biology to refer to the "free-feeding" weight of an animal, as opposed, for example, to the weight after a restricted diet. For example, "The rat's ad libitum weight was about 320 grams." In nutritional studies, this phrase denotes providing an animal free access to feed or water thereby allowing the animal to self-regulate intake according to its biological needs. For example, "Rats were given ad libitum access to food and water."

In biological field studies it can also mean that information or data was obtained spontaneously without a specific method. Medical prescriptions may use the abbreviation ad lib. to indicate "freely" or that as much as one desires should be used.


In drama, the quick-witted invention of dialogue to cover a performer's memory lapse would be described as an ad-lib. Or, a director might encourage performers to ad-lib in a particular show. The term ad-lib usually refers to the interpolation of unscripted material in an otherwise scripted performance. When the entire performance is predicated on spontaneous creation, the process is usually called improvisation, such as in the show Whose Line Is It, Anyway?.

Live performers such as television talk-show hosts (i.e. Jay Leno, David Letterman, etc.) sometimes enhance their reputation for wit by the delivery of material that sounds ad-libbed but is actually scripted, and may employ ad-lib writers to prepare such material.

It is a common misconception that "ad lib" stands for 'adding liberally'. However, although it may hold the same meaning, the origin is not true.

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