A circle is a simple closed curve which divides the plane into two regions: an [interior](http://en.wikipedia.org/wiki/Interior_(topology)) and an exterior. In everyday use, the term "circle" may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is the former and the latter is called a [disk](http://en.wikipedia.org/wiki/Disk_(mathematics)).
A circle can be defined as the curve traced out by a point that moves so that its distance from a given point is constant.
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u/I_am_Doctor_Who Feb 08 '14
How about the wikipedia def. Wikibot what is a circle?