Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the meaning “alteration”.

Parallax scrolling is a special scrolling technique in computer graphics, wherein background images move by the camera slower than foreground images, creating an illusion of depth in a 2D video game and adding to the immersion.

Astronomers use the principle of parallax to measure distances to the closer stars. Here, the term “parallax” is the semi-angle of inclination between two sight-lines to the star, as observed when the Earth is on opposite sides of the Sun in its orbit. These distances form the lowest rung of what is called “the cosmic distance ladder”, the first in a succession of methods by which astronomers determine the distances to celestial objects, serving as a basis for other distance measurements in astronomy forming the higher rungs of the ladder.

Parallax design gives websites a great opportunity to:

1. Wow viewers with page depth and animation
2. Take a story-telling approach to guide visitors through the site
3. Make page visits last longer by encouraging visitors to scroll through the entire page
4. Provoke curiosity