IANA later added these top level domains:
Below all of these top level domains reside all the other domains. These top level domains ‘delegate’ the authority to manage the domains to the owner of the second level domain. By way of example: I have been delegated authority over the inetdaemon secondary domain under .com. The United Kingdom has delegated .uk to the second level ‘company’ domain of .co, so UK companies are typically co.uk.