Over the years in various countries alternative domain registries have been established to allocate domains under domain hierarchies (typically second-level domains) which compete with official gTLDs and ccTLDs.
Independent Domain Registries are not accredited by ICANN. They get their name space from a gTLD or ccTLD registry by registering a domain which resembles an official hierarchy. An example of this would be to register UK.COM with Network solutions which would allow you to allocate domains like example.uk.com. This domain resembles the equivalent issued by Nominet, e.g., example.co.uk.
Most of the Independent Domain registries operate due to having a domain which starts with an ISO 3166-1 code and then is in a gTLD hierarchy such as .COM.
