What is an IP address?
An IP (Internet Protocol) address is a number that identifies each computer connected to the Internet and, more generally, the network interface of the computer equipment (personal computer, smartphone, router, printer, ...) connected to a computer network using the Internet Protocol.
Thanks to the to IP traces backed-up on servers, the authorities can identify people practicing unauthorized actions on the Internet for instance.
There are two versions of IP: version 4 and version 6. IPv6 has been introduced to replace IPv4 that reached saturation in 2011.