IP address
From Just Solve the File Format Problem
An IP address is a number that identifies an Internet Protocol (IP) source or destination. In most cases, it is globally unique.
IP addresses currently come in two varieties: 32-bit IPv4 addresses (consisting of four bytes worth of numbers generally expressed as a dotted-decimal like 123.45.67.89; this address space is running out due to the vast expansion of the Internet), and 128-bit IPv6 addresses (large enough to give every person in the world trillions of addresses, which could be needed for all the nanomachines of the future). The address expansion of IPv6 is a useful thing, but it is still taking many years to complete the transition, and most current Internet activity is still in the old address space.
