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Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

Are there any differences between 'oval' and 'ellipse'?.
Output:
I believe they can be used interchangeably in common English, but have specific (and different) meanings when used in mathematics. The online Cambridge dictionary contains the following definitions: Oval shaped like a circle that is flattened either at one place or at two opposite places, so that it is like either an egg or an ellipse Ellipse an oval; a flattened circle However, in geometry there is a difference. According to the Wikipedia page on ovals: In geometry, an oval or ovoid is any curve resembling an egg or an ellipse, but not an ellipse. In addition, from the Math Forum once the size of an ellipse has been fixed then its exact shape is mathematically determined. In other words, the line forming the perimeter can be drawn in only ONE way. This is distinct from an oval where the perimeter has only to be a concave curve, and there are many possibilities. Simply, an ellipse IS an oval, but an oval may or may not be an ellipse. Doctor Sarah, The Math Forum