An internet domain, or sometimes a domain name, is an identifier of either an entire computer network or a specific computer connected to the internet.
An internet domain is divided into several parts, which are organized into levels. As an example, take www.cs.mujweb.cz. For clarity, the numbering is sometimes counted from the end. In the example above, .cz is a first-level domain, mujweb is a second-level domain, cs is a third-level domain, and so on. A domain is part of a hyperlink.
Use
Each domain can be used only once. Domain names are overseen by IANA, which, among other things, ensures that no domain names are duplicated and also approves first-level domains, of which there is a limited number.
Only a small part of the alphabet (the English alphabet) can be used in a domain name. There have also been attempts to introduce diacritics into domain names, but this caused problems and was abandoned. Each part of a domain name can be only 63 characters long. Overall, a name can be at most 255 characters long.