One IP address (regardless of url) making more than 20 requests/second, evaluated over a 10 second window. Practically speaking, this means if you make 400 requests in 8 seconds, that's fine, but if you make 400 requests over 12 seconds you'll exceed the window and get rate limited.

The same request (regardless of IP address) being made more than 20 requests/second, evaluated over a 10 second window. Same rules apply as above.