A domain name is a way to identify and locate computers and resources connected to the Internet. No two organizations can have the same domain name.
Every company or organization that wants to be on the internet will register a domain name for use as their on-line identity or name that clients will use to access on-line services such as the organization's website or email system.

Domain name is a unique name that identifies a website.

A domain name is an identification string that defines a realm of administrative autonomy, authority or control within the Internet.

Domain name is like your home address