A domain is the name of your website. It is the address used to visit your site within a browser. The domain looks like this: https://www.DOMAIN.com This sites domain name is 2upnorth and it typed in http://2upnorth.com
All domains must be registered with a hosting company and renewed each year. So you own it as long as you continue to pay for it. If you stop paying for it, most domain companies give you quite a few announcements to allow you to keep it if you fall behind. Good thing is they aren’t very expensive and only need to be renewed once a year.
The only way to get to your website is by your domain.