What does it mean for an actor to be "off-book"?

Being "off-book" means that an actor has memorized their lines and no longer requires the script during rehearsals or performances. This is an important milestone in the rehearsal process, as it allows the actor to focus on their performance rather than having to read from the script. When an actor is off-book, they can better engage with their fellow cast members and respond to cues and emotions more naturally, leading to a more polished and dynamic performance.

In contrast, the other options refer to different stages of rehearsal or performance. Being fully rehearsed with the entire cast implies a level of coordination and familiarity with both lines and blocking, but does not specifically highlight the memorization aspect that defines being off-book. Acting without costumes is related to dress rehearsals and has no bearing on an actor's readiness in terms of memorization, and practicing with the script indicates that the actor is still reliant on the text for their performance, which means they are not off-book.