Ellipses also have 2 points known as the foci. As demonstrated in the picture to the left, The sum of the distance from these two points (d1 + d2) is always a constant (2a). This is essentially what makes an ellipse. Also, the distance from the focus to the center is known as c..
Important: It is significant to know the eccentricity regarding an ellipse. Eccentricity is how round a conic is, 0 being perfectly round. An ellipse's eccentricity is greater than 0 but less than 1. This could be written as e = 0 < x < 1. This is because an ellipse isn't perfectly round like a circle (whose eccentricity is 0) and yet it is more round than a parabola (whose eccentricity is 1). Eccentricity could be found by dividing 'c' by 'a' (c/a).
3). Real World Application: Elliptical Training Machinery
Elliptical gym equipment, such as elliptical runners/climbers are very useful when trying to avoid joint injury in a workout. Basically, the elliptical motion which is usually amplified with the use of handle bars or a motor drive, limits the impact on the joints that is very common with running. This article outlines this use for ellipses as well as a few other uses: http://www.ehow.com/info_8522010_real-life-uses-ellipses.html
...And this is a guy with a cool accent who will transmit elliptical knowledge to your brain in a brief 2 minutes:
4). URLs cited : Pictures from the top-down:
Youtube video link: https://www.youtube.com/watch?v=AVrUEAiw5gA