AAAA is a domain name record, that's in essence the IPv6 address of the server in which the domain name is hosted. The IPv6 system was designed to replace the present IPv4 system in which every IP is comprised of four groups of decimal numbers ranging from 1 to 255 e.g. 126.96.36.199. In comparison, an IPv6 address has eight groups of four hexadecimal numbers - from 0 to 9 and from A to F. The reason behind this transformation is the tremendously smaller selection of unique IPs the current system supports and also the speedy increase of devices that are connected to the Internet. A good example of an IPv6 address would be 2101:1f34:32e2:2415:1365:4f2b:2553:1345. If you want to forward a domain name to a machine which uses such an address, you will have to set up an AAAA record for it, and not the commonly used A record, that is an IPv4 address. The two records provide the very same function, but different notations are used, to separate the two forms of addresses.