IPv6 - Internet Protocol Version 6

Internet Protocol Version 6 (IPv6) is a version of the Internet Protocol that is designed to succeed Internet Protocol version 4 (IPv4). IPv4 was the first publicly used Internet Protocol and has been in operation since 1981.

IPv6 is an Internet Layer protocol for packet-switched internetworking and provides an end-to-end datagram delivery service. The main driving force for the redesign of Internet Protocol was the foreseeable IPv4 address exhaustion. IPv6 was developed by the Internet Engineering Task Force (IETF), and is described in Internet standard document RFC 2460, published in December 1998.

IPv6 uses a 128-bit address, whereas IPv4 uses only 32 bits (2^32 addresses). The new address space supports 2^128 (about 3.4×10^38) addresses. This expansion provides considerable flexibility in allocating addresses and routing traffic. It also eliminates the primary need for network address translation (NAT), which gained widespread deployment as an effort to alleviate IPv4 address exhaustion.
Source: Wikipedia