1. (verb) To speak, perform, or act without preparation or written script; to improvise
The actor had to ad-lib when he forgot his lines.
O ator teve que improvisar quando esqueceu suas falas.
2. (noun) Something said or done without preparation; an improvisation
His funny ad-lib got a big laugh from the audience.
Seu improviso engraçado arrancou uma grande risada do público.
3. (adjective) Done or said without preparation; improvised
She gave an ad-lib speech at the wedding reception.
Ela fez um discurso improvisado na recepção do casamento.