Difference between front end and back end of web page?

I've never heard those terms applied to a web page. Generally front and back ends are terms applied to a database. The back end is just the data tables. The Front end is everything else; Forms, reports, menus, etc.

Now a WEB page could be a front end to a database. For example, this site is a front end to a database of notes.

I've used front end and back end for web pages before, it just seemed natural when dealing with PHP and mySQL.

Here's what I consider them:
The front end of the page is what the user sees. The forms on the page, the graphics, the HTML and CSS.

The back end, I see as the scripting. If you've got a PHP script that pull from a database, or reads from certain files, or performs calculations based on input, that would be the back end. Maybe some javascript that takes data from some forms on the page and parses it into another form of output. The part a normal user won't see, but is happening in the background to make the site work.