'Tech crew' is the more official name for theatre techies. These are the people who run just about everything technical in a theatre. They can often be divided up into various sub-crews:

Stage Crew - Led by the Stage Manager, the stage crew take responsibility for everything on the stage itself.
Lighting Crew - Led by the Chief Electrician, the lighting crew do... ummm... lighting?
Sound Crew - I'm not sure what these people do. Someone tells me it's something to do with sound - I'm not so sure myself. The person in charge is normally a Sound Engineer.

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If you're after any other theatre tech information, then do take a look at 'Everything you ever wanted to know about theatre tech, but were afraid to ask'

Theatre technicians often have colorful nicknames for each other. Like most nicknames they can be highly offensive, merely humorous, or even respectful depending on the attitudes of the person using them and the person being refered to. Some of these names include:

Electricians=
Squints, FITWE (pronounced Fit-Wee, and short for Freakin' In The Way Electricians), Sparkies

Sound Techs=
Hum Heads, Noise Boys, Soundinistas

Carpenters=
Carps, Wood Butchers, Hammerheads

Props Crew=
Prop Tarts, Proptologists