What is meant by "On the book" in the context of acting?

The phrase "on the book" refers to the practice of using a script during a performance. This often occurs during rehearsals or performances where the actor has not yet fully memorized their lines. It allows performers to stay connected to the text while still engaging with their character and the audience. This practice ensures that the actor can accurately deliver the lines and adhere to the flow of the script, especially in complex scenes or when new material is being introduced. Additionally, it serves as a valuable tool for less experienced actors or in productions that require a quick turnaround for performances, ensuring that all performances maintain consistency and clarity until lines are fully memorized. Utilizing the script can also provide assurance for the actor, allowing them to focus more on their performance without the added pressure of memorization, especially in early rehearsals.