Apps?

I realize that I am hopelessly behind the times when it comes to smart phones, but in an effort to keep up, I'm doing this self-paced library program called 23 Mobile Things.  The first thing I'd like to find out is what is an app and how is it different from a regular webpage. I purchased a very inexpensive tablet that works with Android so I'm hoping to use this device to discover what apps are and how to use them.

I should also note that I went through the 23 Things on a Stick 5 years ago and learned a great deal--I can't say I've totally mastered web tools, but I have a much greater understanding of what is out there thanks to this program.  I originally set up a blog called 23 Ways of Looking at a Library for that program so this blog is 23 New Ways of Looking at a Library.  I look forward to re-acquainting myself with blogging as I investigate these mobile thing.