What is an I.P. Address?

Each computer on the Internet has an IP address that uniquely identifies it from all other computers on the Internet. When you send or receive data, the message gets divided into little chunks called packets. Each of these packets contains both the sender’s Internet address and the receiver’s address. And is sent first to a gateway computer (which is normally a networking device named router) that understands a small part of the Internet. The gateway computer reads the destination address and forwards the packet to an adjacent gateway that in turn reads the destination address and so forth across the Internet until one gateway recognizes the packet as belonging to a computer within its immediate neighborhood or domain that gateway then forwards the packet directly to the computer whose address is specified.

IP stands for Internet protocol, and these addresses are 32-bit numbers, normally expressed as 4 "octets" in a "dotted decimal number." A typical IP address looks like this:

192.168.0.1

The four numbers in an IP address are called octets, . 
Every machine on the Internet has a unique IP address. A server has a static IP address that does not change very often. A home machine that is dialing up through a modem often has an IP address that is assigned by the ISP when you dial in. That IP address is unique for your session—it may be different the next time you dial in. This way, an ISP only needs one IP address for each modem it supports, rather than for each customer.