Refers to the 4th revision of the Internet Protocol, where addresses are usually displayed in the form of dotted decimals between 0-255. Ex: 169.254.0.1

The IP address of a device is its unique identifier on a network which allows communication with that device.

Given the fact that only 2^32 IPs are available, number which is already depleted, its successor (IPv6) has officially taken over on 6 June 2012.