Ad libitum  Ad libitum () is Latin for "at one's pleasure" or "as you desire"; 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:  Note that the direction "a piacere" (see above) has a more restricted meaning, generally referring to only the first two types of discretion. Baroque music, especially, has a written or implied "ad libitum", with most composers intimating the freedom the performer and conductor have. For post-Baroque classical music and jazz, see cadenza. The Reverend Samuel Danforth Jr. published a poem titled "Ad Librum" in the 1686 edition of the New England Almanac. "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 or pair feeding. For example, "The rat's "ad libitum" weight was about 320 g." 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 were 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. More common is "pro re nata" dosing, in which a drug is used only if needed and only up to some maximum amount. Ad-lib is used to describe individual moments during live theatre when an actor speaks through their character using words not found in the play's text.