If you click on the question mark in the top right corner you will get the definitions. More documentation is in the source code.
EDIT: As I say in the "warning" section of the readme file: usually it's not a good idea to show the raw data because it will confuse the end user. And if you add more explanation you will cause clutter and cognitive overload. I show the raw data mostly for people that want to dig into the source code.
On the topic of confusion, I think your demo would be clearer if you renamed "News stories bottom average score" to "Front page stories bottom average score". News is just a little too close to Newest, so I had to reread the definitions of both a couple of times. Cool project otherwise!
EDIT: As I say in the "warning" section of the readme file: usually it's not a good idea to show the raw data because it will confuse the end user. And if you add more explanation you will cause clutter and cognitive overload. I show the raw data mostly for people that want to dig into the source code.