What do you mean by Domain Name?
While there are many definitions for Domain Name, as per TechTarget definition:
A domain name locates an organization or other entity on the Internet. For example, the domain name
locates an Internet address for "totalbaseball.com" at Internet point 220.127.116.11 and a particular host server named "www". The "com" part of the domain name reflects the purpose of the organization or entity (in this example, "commercial") and is called the top-level domain name. The "totalbaseball" part of the domain name defines the organization or entity and together with the top-level is called the second-level domain name. The second-level domain name maps to and can be thought of as the "readable" version of the Internet address.
On the World Wide Web your domain name is your own unique identity. No two parties can ever hold the same domain name simultaneously; therefore your Internet identity is totally unique. A domain name gives your website as well as your email a proffessional look.
So, basically, it’s the identity of your website. Your website is incomplete without a domain.