A domain is a human-readable Internet address. Instead of typing a numeric IP address, users can visit a website or send email using a name that is easier to remember.
A domain is made of different parts. In example.com, "example" is the second-level domain and ".com" is the extension, also called top-level domain.
Domains are managed through DNS, the system that connects the name to web servers, email servers and other online services. Owning a domain does not automatically mean having a website: hosting, email and DNS configuration are separate services.
A good domain can become a brand asset. It can improve memorability, trust, direct traffic and the perceived authority of a project.