Strings of letters and numbers (separated by periods) that are used to name organizations and computers and addresses on the internet WordNet 3.0 & Open English WordNet

In the Internet, a domain name is a string that identifies a realm of administrative autonomy, authority or control. Wikipedia

A label that identifies a realm of administrative autonomy, authority, or control within the Internet Wikipedia Disambiguation

Identification string that defines a realm of administrative autonomy, authority or control within the Internet Wikidata

A domain; that part of a domain name which (nominally) identifies an organization; a domain name delegated to an independent administrative authority who is then responsible for the management of that portion of the Domain Name System's namespace that consist of the delegated domain and all subdomains that are not delegated in turn. Wiktionary

Part of a domain name. Wiktionary (translation)