Ad libitum - a phrase translated from Latin meaning “at will”, “at one’s own discretion”. In musical notation, the indication Ad libitum means that the performer is given the freedom to choose the nature of the performance - tempo, dynamics (for example, F. Liszt's symphony “Faust” with the final ad libitum choir). The term is used both in theater and oratory. In medical prescriptions, the abbreviation ad lib. means that the medicine or its component can be used in any quantities.
An ad libitum example: if an actor in a theater has forgotten part of his monologue or dialogue , he can quickly figure out how to replace the missing phrases so that no one notices anything. Moreover, sometimes the directors insist that the actors come up with some fragments in the production on the go, thus performing them ad libitum .
The term ad libitum usually refers to the interpolation of a missing piece of material in the context of an otherwise fixed play. If the whole production is entirely based on creating material during the performance, the whole process is usually called improvisation (as in the cinema).
Television presenters sometimes insert into their performances memorized texts that look like an impromptu ad libitum performance, but are actually invented and recorded in advance.
In music, the term ad libitum is also used to refer to improvised parts of a work. This term as an instruction to the performer can even be recorded in musical notation.
In scientific studies of the effect of calorie restriction diets on the lifespan of model animals (nematodes, Drosophila, mice, primates, etc.), the term ad libitum or, in short, AL , is applied to the control group of animals receiving an unlimited diet. Animals receiving a calorie-restricted diet (typically 30%) are designated CR (caloric restriction).