URL is the abbreviation of the words Uniform Resource Locator whch is the global address of documents and other resources on the World Wide Web. Think of it like your address for your house. The only way anyone could find your home is if they had your address. And there is only one of these addresses. It is unique.
Your URL is the address for your website.
.com, .org, and .net are sample extensions of your www.___________ URL (address)