Titles are from a line Sharpay Evans says in High School Musical 3: Senior Year. Four years of highschool drama club has led me to this. I'm sure my directors are so proud. 

Theatre Term Glossary

matinee- A performance (or movie) that is done in the daytime. Matinee showings have lower ticket prices than night time showings.

performing arts center (PAC)- Basically an auditorium but fancier. 

running crew-A tech team whose main job is to move (run) the set (setting/scenery) pieces in-between scenes as quickly as possible. 

pit (AKA orchestra pit)- A small room underneath the stage where the musicians play, led by a conductor. In highschool musicals, the pit is typically comprised of a couple kids from band or orchestra. A professional pianist is often hired to do the piano accompaniment. 

chorus-(Typically) unnamed characters that sing accompaniment to the lead characters. Some chorus members may have a few lines of dialogue, or a special part in a song/dance. If needed, one actor can play multiple chorus parts--just not in the same scene. In larger musicals, majority of the cast are chorus members.

techies- Members on the technical crew. Almost everyone works backstage.