Do ellipsoids have eccentricity?

Question

I'm trying to build a program to represent ellipsoids for a class I'm taking, and part of the problem is that we have to use inheritance. Basically, I have to start with a representation of an ellipse, then use that to make a representation of an ellipsoid. One of my parameters for building an ellipse is the eccentricity, which I learned from precalculus to be a measurement of how close to a circle that an ellipse is (or the ratio of the distance from the center to the foci and the distance from the center to the vertices). I'm assuming that ellipsoids have a similar property for how close they are to a sphere, but I'm not sure what it is as google doesn't come up with useful results. Is there a different name for this? How do I find the "eccentricity" of an ellipsoid?