What is an Internet Protocol (IP)?

Each computer (also known as a host) on the Internet has at least one IP address that distinctively identifies it from all other computers on the Internet; the method by which data is sent from one computer to another is known as the Internet Protocol (IP).

Data which is sent or received (e.g. an e-mail or a Web page), gets divided into little pieces called Packets. Each packet contains both the sender’s Internet address and the receiver’s address.
All packets go through a network of gateway computers, and each of these computers understands only a small part of the Internet; when a computer receives a packet, it reads its destination address and forwards the packet to an adjacent gateway that repeats the same action, until the packet reaches a gateway which identifies it as belonging to a computer within the immediate neighborhood or domain. The packet is then forwarded directly to the computer whose address is specified.

Since any given message gets split to a number of packets, it is possible that each packet would be sent via an altered route, if needed, and that the packets would reach their destination in a different order than the one they were sent in. Up until this point, it was the Internet Protocol’s responsibility to deliver the packets; at this stage, it is the Transmission Control Protocol’s (TCP) job to put them back in the right order.