What is a URL?
Internet Marketing Dictionary | URL

A URL is simply the address of a web page and can be entered into the address bar of your browser when you want to see the underlying page.

When you enter a URL or click on a link, your browser essentially goes out to the internet to find the file that corresponds to that URL's address and fetches a copy of it for display. The file itself will then be interpreted by your browser software (Firefox, Safari, Operal Internet Explorer etc.) so that you see the web page in the way the designer intended.

A URL does not need to point just to a web page though. It can point directly to a pdf file, or a music file or video. Or even a text, Word or Excel document.  So if you want to make a Word document available on the internet all you need to do is upload it to your server. Once you've done that, anyone clicking on a link to that file or just entering it into the address bar of their browser will be able to download it.

One problem with URLs is that people move files around from time to time and delete them too which means that quite often the file you are looking for doesn't exist anymore or has been moved. This typically generates a 404 error page which is essentially a message that tells you that the file you want can't be found.