Of late you must have noticed on some blogs and websites that not all the images load with the current page. They begin to load as you reach that particular area. This is called lazy loading.
If a particular blog post or a webpage contains lots of images it may take a long time for the page to load and this may distract people. This also needlessly wastes your bandwidth if people are never scrolling down to particular areas. In conventional web design whether there is a single image or 20 images on a webpage all the images are loaded. This wastes time as well as bandwidth. Lazy loading on the other hand involves showing the images only when the person has reached that particular area.
This blog post on Speckyboy explains to you how to lazy load images on your website or blog.