An IP address is a unique number, akin to a telephone number, used by machines (usually computers) to refer to each other when sending information through the Internet using the Internet Protocol. This allows machines passing the information onwards on behalf of the sender to know where to send it next, and for the machine receiving the information to know that it is the intended destination.
An example IP address is 188.8.131.52. Converting to such numbers from the more human-readable form of domain addresses, such as www.wikipedia.org, is done via the Domain Name System. The process of conversion is known as resolution of the domain name.