A domain name registrar is a service that helps you to sign your chosen website domain name legally so that it is unique to you and nobody can own it.

The Internet Corporation for Assigned Names and Numbers (ICANN) accredits the legitimate domain name registrars. ICANN is a private (non-governmental), non-profit corporation in charge of allocating IP addresses and controlling the Domain Name System (DNS). The DNS is what enables you to access a website by typing in its name, rather than its numerical IP address. (What Is a Domain Name Registrar?, 2020)