Simply put, a Domain Name is the name of a website. It is what comes after “@” in an email address, or after “www.” in a web address. It is what you type in your browser when you want to go to a website: e.g. mydomain.com
A Domain Name can be used to identify a single IP Address or a group of IP Addresses. While computers require IP Addresses to locate one another, we humans use Domain Names. This purely numeric IP Address is converted to a readable and recognisable, alphanumeric Domain Name by a system known as the Domain Name System (DNS).
To make it easier for you, think of the Domain Name as your phone number, and the website as your phone. They may be connected, but they are two separate items. Hence, you can change your phone (website) at any time, and keep your existing phone number (Domain Name), so you can still connect it to your new phone (new website). That being said, it is implied that your Domain Name may not be permanently stuck in only one specific website. You can disconnect it and reconnect it to any other website of your choice.
Note: Your Domain Name can be connected to only (1) one website at a time.