A number, by which a computer can be identified should it attempt to communicate via Internet Protocol.
Usually shown as four groups of up to three digits (like so: 127.0.0.1).
Because IP address are hard to remember for humans we use things calles URL's instead.
When one types in a URL like www.arrse.co.uk, your computer goes to a central phonebook of sorts and that phone book says that www.arrse.co.uk = 126.96.36.199
as you can see www.arrse.co.uk is far easier to remember that 188.8.131.52.