AAAA is a domain address record, which is in essence the IPv6 address of the server where the domain is hosted. The IPv6 system was introduced to replace the existing IPv4 system where each and every IP address is comprised of 4 sets of decimal numbers which range from 1 to 255 e.g. 188.8.131.52. In comparison, an IPv6 address has 8 sets of 4 hexadecimal digits - ranging from 0 to 9 and from A to F. The reason behind this change is the tremendously smaller amount of unique IPs that the present system supports as well as the rapid increase of units which are connected to the Internet. An illustration of an IPv6 address would be 2101:1f34:32e2:2415:1365:4f2b:2553:1345. If you'd like to direct a domain name to a machine which uses such an address, you will have to set up an AAAA record for it, not the widespread A record, that is an IPv4 address. Both records deliver the same exact function, yet different notations are used, to distinguish the two forms of addresses.