IDN TLDs

Internationalized Domain Names contain characters that are outside the usual alpha-numeric character set. They contain characters with accents or non-English entities.

Because labels within the DNS are encoded in ASCII, these types of entities must be converted to an ASCII representation before they can be used within the DNS system. This is facilitated by converting them to punycode.

Punycode uses a function called to ASCII to strip out the characters that need encoding and appends them to the remaining string separated by a hyphen. (The entire encoding process is described in RFC 3492.) Take a look at this:

In other words:  would become motorhead-p4a, then we also need a mechanism to signal that this label or domain was not originally an ASCII label to begin with, so the prefix xn-- was selected.

Thus, Motorhead.com becomes xn-motrhead-p4a.com (alas, that domain is already taken).