Which term is used to describe an actor who must use a script during a scene?

The term used to describe an actor who must use a script during a scene is "On the Book." This phrase indicates that the actor relies on the written material during their performance, often because they are still learning their lines, have not yet fully memorized the script, or are still in the rehearsal process. Working "on the book" can be common in early rehearsals, as it allows actors to focus on their delivery, blocking, and characterization while still having the text as a reference.

The other terms have distinct meanings in theater. "In Character" refers to an actor fully embodying their role, making choices based on their character's motivations and background, typically performed without reliance on the script. "In Rehearsal" describes the process of preparing and refining a performance, during which actors may still use scripts but aren’t acting in front of an audience. "Off Script" indicates actors performing their lines from memory, having moved beyond the need for the script.