Frontend & browser·Loading, assets and the critical path
you optimise only what is visible before any scrolling and let everything below load later.
Above the fold
Also calledinitial viewport, first screen
The part of the page visible in the viewport before the user scrolls, which is what every first-paint metric measures. It is device-dependent and, on a long page, a small fraction of the document, which is what makes deferring the rest so effective. The term is borrowed from newspapers and is imprecise on purpose: the useful version is 'what the browser must have to paint the first screen'.