Above the fold is an expression used to represent the portion of a webpage that a visitor will see immediately upon loading. The area that you see before needing to scroll down to see is considered above the fold. The “fold” can vary based on screen size/resolution and device type. It is common practice to optimize web pages and landing pages for the most common screen sizes (resolution) to improve functionality. To find the most common screen sizes used visit this resource on browser display statistics.
Also check out: below the fold.