A “breakdown” is industry parlance for a list of the characters in a script that a casting director is looking to cast. Actors and their agents read the character descriptions in a breakdown to see if there are any roles they should audition for.
Breakdowns can range in size from one sentence to a whole paragraph. Here’s one:
DENNY – Male, 18 to play 15-18, open ethnicity. Asthmatic, heavy breathing, loud, overly nerdy, & socially awkward. He could tell you what Captain Kirk said in scene three, line two, of episode 43. Improv experience preferred. Knowledge of comic books, video games, computers, & anything geeky preferred.
And here’s another one. It’s shorter, but you still can get a sense of what they’re looking for:
JONES – African American male. Age late 30’s to early 50’s. He is Taja’s ‘bad boy’ boyfriend.