AAAA is a domain name record, which is in essence the IPv6 address of the server in which the domain is hosted. The IPv6 system was introduced to replace the current IPv4 system in which every single IP address is made up of four groups of decimal digits between 1 to 255 e.g. 5.168.208.143. However, an IPv6 address includes 8 sets of four hexadecimal digits - from 0 to 9 and from A to F. The reason for this transformation is the significantly smaller amount of unique IPs the existing system supports and the fast 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'd like to direct a domain to a web server which uses such an address, you'll have to set up an AAAA record for it, not the widespread A record, that is an IPv4 address. The 2 records deliver the same exact function, but different notations are used, so as to identify the two forms of addresses.