1. Tool. Replaceable, interchangeable working end of a rotary tool. Drill bit, router bit, screw bit.
2. Acting. Piece of onstage business or routine. Comedy bit. From http://comedians.about.com/od/glossary/g/bit.htm :
3. Equestrian. The metal part of a horse's bridle that goes in the mouth. Bit and bridle.
4. General. A small amount. Director to LD, "Can we have the cyc just a bit more green?" LD to Director, "We can, but seeing as how I have zero green cyc lights up there, that's going to be a bit of a challenge."
5. Electronics/Computers. One digit in a binary string. Can either be one (known as true) or zero (known as false). Similar concept in digital electronics, a one value being the presence of a signal, zero being the lack of a signal.