Domain Name

A domain name is the name of a website. It consists of a series of "labels" (separated by "dots").

The ASCII form of an IDN label is termed an "A-label". All operations defined in the DNS protocol use A-labels exclusively.

The Unicode form, which a user expects to be displayed, is termed a "U-label". The difference may be illustrated with the Hindi word for "test" — परीक्षा — appearing here as a U-label would (in the Devanagari script). A special form of "ASCII compatible encoding" (abbreviated ACE) is applied to this to produce the corresponding A-label: xn — 11b5bs1di.

A domain name that only includes ASCII letters, digits, and hyphens is termed an "LDH label". Although the definitions of A-labels and LDH-labels overlap, a name consisting exclusively of LDH labels, such as"icann.org" is not an IDN.