The LaziestLoader plugin allows content to be loaded on a page only when the user directly views it by scrolling down to it.
Basically the plugin loads only content visible on the screen (viewport). When the user scrolls down to view some more content, that content is loaded then and only then.
This makes large, long Web pages load much faster, increasing overall site loading speed and indirectly SEO parameters.
A demo and lots of documentation is included with the download package. Requirements: