A ccTLD, an abbreviation of country code top-level domain, is an extension that is assigned to a country in the world. 
Every country has its own domain extension based on the ISO 3166 alpha-2 Country codes. Examples of of ccTLDs include: .uk (United Kingdom), .us (United States), .in (India) etc.

A popular country code extension is ’.tv’ which is the extension for the small nation of Tuvalu and makes the nation approximately $5 million USD per year.