Learn English – word for a class of circular shapes

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I'm not sure if this belongs here, but I'm wondering if there is a word for a class of circular shapes?

Thinking about this hierarchically:

* Shape
  * Polygon
    * Square
    * Rectangle
  * ???????
    * Circle
    * Oval

EDIT:

Ok, so mathematically I'm not sure there is a correct answer to my question that's any better than the one Mehper so eloquently explained (round shape). Let's break down what we have so far:

In the blue corner: Noldorin

* Ellipsoid
  * Ellipse
    * Circle
  * Oval

In the red corner: pretty much everyone else

* Oval
  * Ellipse

Now, my question for the red team is: where does a circle fit in? From what I understand a circle can't be an oval, but a circle is an ellipse. Those two facts make the following untrue:

* Oval
  * Ellipse
    * Circle

I'll stick with ellipsoid for now until I hear some better explanation.

Also note this link: http://en.wikipedia.org/wiki/Ellipsoid#Egg_shape

An egg shape, which is an oval (not an ellipse) is comprised of two ellipses. This seems to make an oval a sub-class of an ellipse.

Kindly correct me if I've made any mistakes.

Best Answer

Circles and ovals are both types of ellipses. An 'oval' is really the informal term for an 'ellipse', whereas a 'circle' is an ellipse where the semi-major and semi-minor axes are equal.

If you're talking about higher-dimensions, the word you are looking for is probably ellipsoid. (A sphere is an example.)

Edit: I'm not sure what I exactly I was imagining in terms of "oval" at the time, but I was probably wrong to call it a type of ellipse. In fact, it does not have a precise mathematical definition, so saying one is a type of the other doesn't make much sense either way. All it means is, loosely, "egg-like" in shape. A circle, however, is a specific type of ellipse, as mentioned originally.

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