A domain name is the internet equivalent of your home or business address. It is used in order for people to find your website on the internet.
Each domain is made up of a suffix called a Top Level Domain or TLD (e.g. .com, .co.uk, etc.) followed by a minimum of a second level domain (e.g. my-domain-name).
There are a multitude of TLD’s to choose from nowadays, but in the early days of the internet there were only a few, such as .com and .org. This is the main reason why the .com still remains so popular today.
Your domain name would be a word or phrase followed by a TLD, for example, mydomain.com. The mydomain bit is your domain name as is technically referred to as a second level domain name.
So most domains look like second-level-name.top-level-domain.
It’s also worth noting that you cannot have spaces in a domain name, as a rule you would eliminate them from a phrase altogether or replace them with dashes (-).