出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/02/19 21:03:07」(JST)
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An oval (from Latin ovum, "egg") is a closed curve in a plane which "loosely" resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition. In common English, the term is used in a broader sense; any shape which reminds one of an egg. The 3dimensional version of an oval is called an ovoid.
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The term oval when used to describe curves in geometry is not welldefined, except in the context of projective geometry. Many distinct curves are commonly called ovals or are said to have an "oval shape". Generally, to be called an oval, a plane curve should resemble the outline of an egg or an ellipse. In particular, the common traits that these curves have are:
Examples of ovals described elsewhere include:
An ovoid is the 3dimensional surface generated by rotating an oval curve about one of its axes of symmetry. The word ovoidal refers to the characteristic of being an ovoid and is often used as a synonym for "egg shaped".
In the theory of projective planes, oval is used to mean a set of n + 1 points in a projective plane of order n, with no three on a common line (no three points are collinear). See oval (projective plane).
An ovoid in the finite projective geometry PG(3,q), is a set of q^{2} + 1 points such that no three points are collinear. At each point of an ovoid all the tangent lines to the ovoid lie in a single plane.
The shape of an egg is approximately half of each prolate (long) and is a roughly spherical (potentially even slightly oblate/short) ellipsoid joined at the equator, sharing a principal axis of rotational symmetry, as illustrated above. Although the term eggshaped usually implies a lack of reflection symmetry across the equatorial plane, it may also refer to true prolate ellipsoids. It can also be used to describe the 2dimensional figure that, revolved around its major axis, produces the 3dimensional surface. Refer to the following equation for an approximation of a 3D egg where the letter "a" represents any positive constant:
In technical drawing, an oval is a figure constructed from two pairs of arcs, with two different radii (see image on the right). The arcs are joined at a point, in which lines tangential to both joining arcs lie on the same line, thus making the joint smooth. Any point of an oval belongs to an arc with a constant radius (shorter or longer), whereas in an ellipse the radius is continuously changing.
In common speech "oval" means a shape rather like an egg or an ellipse, which may be twodimensional or threedimensional. It also often refers to a figure that resembles two semicircles joined by a rectangle, like a cricket infield or oval racing track. This is more correctly, although archaically, described as oblong.^{[2]} Sometimes it can even refer to any rectangle with rounded corners.
The shape lends its name to many wellknown places (see Oval (disambiguation)).
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リンク元  「egg」「ovule」 
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