A lighting bar, in a theatre, is a metal (normally steel or aluminium) bar, usually the width of the stage, on which lights are hung. Some lighting bars are just plain bars, and cables are taped to them. Others have sockets built in, and with a multicore, or multiple plug tails coming out of one end.

If the bar is ready-wired, then it can be a lot more convenient, but is also less flexible - you end up needing lots of short extension cables if you need lights packed together more tightly than the sockets are on the bar. On the other hand, taping your own cables in can be more flexible, it is also a lot more work.

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'