When I think of usability, my thoughts primarily revolve around the ease of use of a system — how it works, what works and what doesn’t. There’s a lot more to it than that.
Recently on Twitter, Jeff Croft mentioned the Terms of Services page of the photo gallery site 500px. That made me think of content usability. You can do all sorts of things to help users get to your content; clever navigation, a good search function, few disturbing items around the content etc. While those definitely add to the overall usability of a website, let us not forget that most people visit our sites for the content.
The user terms page of 500px is focused on the user reading it. Every section is explained in everyday terms, making it very transparent what your rights are when uploading photos.
We spend so much time on making our interfaces simpler — why not think about the content too?