Definition

ccTLD is a top-level domain name that is used to define a domain for a specific country or geographic area. Each country has a dedicated domain name, which is referred to as a ccTLD and is usually two letters long. They are usually assigned to countries based on their country codes.  

Application

ccTLDs are reserved for a country or dependent territory and always consist of two letters, for example .us (USA), .uk (UK) and .br (Brazil). Google and other search engines may use ccTLDs to geo-target a website.