When I was in school, I learned what a circle was. Later, I learned what an ellipsis was. I also discovered that a circle is a particular case of ellipse (both foci at the same location).
Now, I'm pretty sure mathematicians have already studied "generalized ellipsis". I mean ellipses with more than two foci.
What's the name of these mathematical objects?
Some links to studies of these objects will be much appreciated.