The simple answer without getting technical, is that a domain is the name that is typed directly into the Web Browser.
When you “own" a domain, you actually never legally own it, you simply own the rights to what happens when someone types in that address. You own the control and the right to use the name, which really are just a bunch of numbers that have been converted into letters for humans to read easily.
For example, when you type in Google.com, you are taking to Google, without you having to type in one of the many I.P. addresses Google has such as 22.214.171.124. Can you imagine typing in these long numbers every time you visited a website?
That’s why you hear people say, “Just Google it", and don’t hear them say, “Just 126.96.36.199 it!".
So in summary, first letters that are easy for humans to read and remember are inputted, then next they are converted to the actual IP address. This is done by a web browser like Chrome or Opera making requests to a DNS where these records are and translated. You owning the rights to what to do with this name, allows you to dictate what happens with this name (set of numbers) every time anyone in the world inputs those characters.