CAT 5

Cat 5 refers to an 8 wire cable that can be used to carry networking information.  The 8 wires are really four pairs of twisted wire-pairs.  This cable is often called "Ethernet" since it is often used to connect computers, or connect computer to the internet as part of a networking system.

It should be noted that cat 5 cables are finding other uses nowadays also - other than computer networking.  Such cables often find themselves in house or store or work building walls and are also used to telephone wires.  In this case, the telephone companies just view the cat 5 cable as being 4 pairs of twisted wires.  Since there are four pairs of wires, one could use a cat 5 wire to connect up to 4 separate phone lines in that house or building.