Lazyload is a jQuery plugin delaying load of images that are out of users sight. This way your page’s visible area is loaded faster.
With lazyload enabled, when user reaches your site, only visible images will be loaded. Images out of sight will be replaced with a placeholder image. When the user scrolls down, jQuery will replace source back to original. This way your pages will load faster. It will also save bandwith from bouncing users. Here is a demo of the lazyload.
Note. If you are using an image based statistics application like sitemeter or mint, you should get image to visible part of the page. Otherwise you won’t get any statistics from users that never reach the footer.
To enable lazyload on your wordpress site, you can either install this jquery plugin manually or you can get wordpress plugin for lazyload. Using the plugin is quite simple, just install & activate.