Definition

A parabola is the set of points on a plane that are equidistant from a given point (focus) and a given line (Directrix)

A real world application of parabolas would be satellites; which is shown in the animation above. Paprabolas can be used in telescopes as well as satellites. the principles are basically the same.

On satellites lines that hit the parabola formed by the dish will bounce into the focus, or the receiver/antenna in the middle.

Telescopes use parabolas to take light and bounce it at the focus. The lenses are shaped like parabolas so they bounce the light rays to a single point (focus).