Above the fold
Above the fold means the part of a page visible before any scrolling - the first screen a visitor sees. The term comes from newspapers, where the top half of the front page (above the physical fold) sold the paper.
The first screen carries disproportionate weight: many visitors never scroll, so what appears there - the headline, the offer, the - often decides whether they stay at all. The fold sits at a different place on every device and depends on the , which is why pages are judged on desktop and mobile separately.