I'm fairly sure it means the entire page. I recently attended a talk given by Mike Magruder about (mobile) performance at Facebook, and a lot of it involved tes

I'm fairly sure it means the entire page. I recently attended a talk given by Mike Magruder about (mobile) performance at Facebook, and a lot of it involved testing the impact of changes on the overall speed of the entire product, this uses the same language, ie referring to Facebook directly when talking about speed. Just a wild stab in the dark on the cause, but maybe a contributing factor is devices that wouldn't load Flash at all take a speed hit from trying to load HTML5 video and the supporting scripts, or maybe the browser doing more heavy lifting rather than offloading it to a plugin?