What is <nav> and <footer>

I've been using framework as a base theme for a couple of years now, and it's been a real joy. Thanks.

I've just started on my first D7 site and grabbed framework to start working. I've noticed the tags and etc and wonder where they come from, and what their purpose is. I'm not seeing it in other themes. Maybe I'm just an idiot and don't know something I should know.

Just want to make sure I don't break the theme before I even start, and use it correctly.