In theater terminology, what does 'ad lib' mean?

In theater terminology, 'ad lib' refers specifically to the act of improvising lines or actions when an actor forgets their scripted lines. This improvisation is often a natural response to the moment, allowing the performer to maintain the flow of the performance and engage the audience even when unexpected situations arise. It demonstrates an actor's ability to think on their feet and adapt to the performance circumstances.

The focus here is on the immediate response to a lapse in memory, which is different from simply rehearsing or performing without preparation or strictly adhering to the scripted dialogue. Such improvisational skills are essential in live theater, where an unexpected situation can occur at any moment, and being able to ad lib helps keep the performance cohesive and engaging.