Country Code Top-Level Domain
Atop-level domain used and reserved for a country or a dependent territory.
These are two letters long, and most of them correspond to the ISO 3166-1 alpha-2 country codes.
There are over 243 ccTLDs.
Most ccTLDs correspond to the two-letter ISO 3166-1 country codes, but there are several differences, explained below.
Each country appoints managers for its ccTLD and sets the rules for allocating domains. Some countries allow anyone in the world to acquire a domain in their ccTLD, for example Austria (at) and Cocos (Keeling) Islands (cc).
Other countries or dependent territories allow only citizens to acquire a domain in their ccTLD, for example Canada (ca).
Lenient registration restrictions on certain ccTLDs has resulted in domain names like I.am, start.at and go.to.
Other variations of ccTLD usage have been called domain hacks, where the Second-level domain and ccTLD are used together to form one word or one title.
This has resulted in domains like blo.gs of South Georgia and the South Sandwich Islands (gs), del.icio.us of United States of America (us), and cr.yp.to of Tonga (to).
(Non country code TLDs have also been used, like inter.net which uses the .net gTLD, probably the first domain hack ever.)