Parallax is a difference in the in the apparent position of an object viewed along different lines of sight. The term derives from the Greek word parallaxis, meaning alteration. In web design, the parallax effect is a relatively new trend. The effect itself has been around for a while, but lately is becoming more used and talked about.
The Parallax effect or parallax scrolling in web design is the technique that features layered images that move around the website in different speeds/perspectives creating a nice and interesting 3D illusion. This effect certainly makes scrolling around websites an interesting experience.
There are many great sites using parallax scrolling out there. From digital agencies using the effect to make it seem as if objects are falling from above, to clothing companies who use parallax scrolling to give visitors an insight into their history. Parallax scrolling has become an exciting way to display content on websites varying in it's complexity and style.