ad libitum (ad lib-i-t<<schwa>>m), adv.[Law Latin]  At pleasure. • The  modern term ad-lib

(adj. & vb.), borrowed from drama and music, is essentially the same; it means “at the performer’s

pleasure,” and allows the performer discretion in innovating a part impromptu.

“[B]ut in actions where the damages are precarious, being to be assessed ad libitum by a jury,

as in actions for words, ejectment, or trespass, it is very seldom possible for a plaintiff to swear to

the  amount  of  his  cause  of  action; and  therefore  no  special bail  is taken  thereon  ….”  3  William

Blackstone, Commentaries on the Laws of England 292 (1768). [Blacks Law 8th]