An IP address is a unique number that every computer connected to the internet is assigned. IP address assignments usually come from your broadband service provider.
IP Addresses work for computers just like phone numbers work for your mobile phone, or like a postal mail address works for your house.
There are two basic types of IP Address assignments:
Static (Always the same address)
Dynamic (Address changes all the time)
Unfortunately, most computers today recieve Dynamic IP Addresses from the broadband ISPs. Just imagine how hard it would be for your postman to deliver your mail if your house address changed every day!
With a Static IP Address, your computer will be reachable at the same address every time.