IPv6 is the abbreviation for Internet Protocol (IP) version 6.
An IPv6 address (e.g. 24da:db8:ac10:fe01:2aa:ff:fe00:56ab) is much longer than an IPv4 address (e.g. 126.96.36.199). It contains a combination of both letters (a through f) and numbers (0 through 9), consists of 32 hexadecimal characters and is 128 bits in length.
IPv6 was necessitated by the phenomenal increase in devices accessing the Internet. Because of this increase, the Internet is running out of IPv4 addresses. The solution is for IPv6 to accommodate this increased demand by providing a larger address space.