1) Ellipse: the set of all points such that the sum of the distance from two points (known as the foci) is a constant
For more information on ellipses, click on the link here or watch the video below:
3) Real World Application: The path of a comet and the orbits of planets, moons, and artificial satellites are all in the shape of an ellipse.
"Planets, moons, comets, and practically everything in the galaxy revolve around a sun in a fixed path or orbit. Earth's orbit is surprisingly more similar to a circle than an ellipse. But many comets and other planets revolve along more stretched out ellipses with a sun near one end rather than in the center. It's as if the sun was twirling everything on a stretchy rubber band that gets longer and shorter again each time the object comes back around the sun.Orbits can also change over a period of many, many years due to gravity. The longer and narrower the orbit is, the longer it takes for the object to make one complete revolution." (http://cse.ssl.berkeley.edu/SegwayEd/lessons/cometstale/frame_orbits.html)
4) Works Cited: