Alrighty, i'm showing up late on this post, but since its an IT question, i'm forced to answer! *ahem*
An IP address is something that your internet service provider uses to recognize you. It can also be used for other people on the internet to recognize you. For example, AIM, ICQ, and MSN are all forms that recognize you by your IP that was given to you.
There's a lot more deeper stuff. There's a MAC address, which is something that your ethernet card has. Each card has its own unique MAC, and networks can use this for further security. MAC addresses can be allowed, and others can be denied. Some networks require you to give your MAC to them in order for you to reach the internet.
Ms. Phoebe M.
IT Tech in training
If any of this information is false, please correct me ^.^ I'm still learning!