One of the “real–world” applications of parabolas involves the concept of a 3-dimensional parabolic reflector in which a parabola is revolved about its axis (the line segment joining the vertex and focus). The shape of car headlights, mirrors in reflecting telescopes, and television and radio antennae (such as the one above) all utilize this property.
In terms of a car headlight, this property is used to reflect the light rays emanating from the focus of the parabola (where the actual light bulb is located) in parallel rays.
This property is used in a converse fashion when one considers parabolic antennae. Here, all incoming rays parallel to the axis of the parabola are reflected through the focus.
Included below is a schematic of the Pluto craft from NASA, which clearly incorporates such a parabolic reflector.
For more information on such work at NASA, I have included the URL for this NASA site. Click here
James A. Sellers