Internet Corporation for Assigned Names and Numbers - responsible for assigning IP addresses.
In order to forward messages to the correct destination, it is essential that each node on the Internet has a unique address. These addresses are known as IP addresses and consist of binary numbers. IPv4 addresses use 32 bit numbers that are usually expressed in dot decimal notation.
In theory, each portion of the address can have a value ranging from 0 to 255 (the maximum number that can be stored in one byte). In practice IP addresses are organised into classes of addresses.
Next: IPv4 Address Classes