What Do Percents Regarding Above-the-fold Content Mean?

UPD I've read related pages carefully, they doesn't answer my particular question. What do the percents mean? Well, there's an attempt at explanation: google page insights will te

Solution 1:

Above-the-fold content is the part of a page you can see without scrolling it down (topmost). How much is that depends on the device, browser size, you name it.

"Approximately 55% of the above-the-fold content on your page could be rendered without waiting for the following resources to load" means just that. In other words "the following resources" has css rules to be applied to 45% of that part of the page (above-the-fold content). The rest (55%) doesn't need external stylesheets. And it probably make sense to move these rules to the page itself and defer loading external stylesheets. So that above-the-fold content could be rendered without waiting for stylesheets to load. It's just that the number (45%) can be grossly inaccurate.