An identifier for a computer or device on a TCP/IP network.

 Networks using the TCP/IP protocol route messages based on 
the IP address of the destination. The format of an IP 
address is a 32-bit numeric address written as four numbers 
separated by periods. Each number can be zero to 255. For 
example, 1.160.10.240 could be an IP address. 
Within an isolated network, you can assign IP addresses at 
random as long as each one is unique. However, connecting a 
private network to the Internet requires using registered 
IP addresses (called Internet addresses) to avoid 
duplicates. 

The four numbers in an IP address are used in different 
ways to identify a particular network and a host on that 
network. Four regional Internet registries -- ARIN, RIPE 
NCC, LACNIC and APNIC -- assign Internet addresses from the 
following three classes. 

Class A - supports 16 million hosts on each of 126 networks 
Class B - supports 65,000 hosts on each of 16,000 networks 
Class C - supports 254 hosts on each of 2 million networks 
The number of unassigned Internet addresses is running out, 
so a new classless scheme called CIDR is gradually 
replacing the system based on classes A, B, and C and is 
tied to adoption of IPv6.

IP address is a unique address for a host to connect in a 
network.IP has two types.one is private add another is 
public add.
it represent 32 bit binary number.it has two name part one 
is anetwork part another is host part.ip add. network part 
is fixed part and host part is unique part.an ip -add. 
controled by IANA-INTERNET ASSIGN NUMBER OF AUTHORITY.
An ip add. is normaly expressed in decimal format.