A **circle** is a simple shape of Euclidean geometry that is the set of all points in the plane that are equidistant from a given point, the centre. The distance between any of the points and the centre is called the radius.

A circle is a simple closed curve which divides the plane into two regions: an interior 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.

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.

A circle may also be defined as a special ellipse in which the two foci are coincident and the eccentricity is 0. Circles are conic sections attained when a right circular cone is intersected by a plane perpendicular to the axis of the cone.

Read more about Circle: Terminology, History, Properties, Circle of Apollonius, Circles Inscribed in Or Circumscribed About Other Figures, Circle As Limiting Case of Other Figures

### Famous quotes containing the word circle:

“Everything here below beneath the sun is subject to continual change; and perhaps there is nothing which can be called more inconstant than opinion, which turns round in an everlasting *circle* like the wheel of fortune. He who reaps praise today is overwhelmed with biting censure tomorrow; today we trample under foot the man who tomorrow will be raised far above us.”

—E.T.A.W. (Ernst Theodor Amadeus Wilhelm)

“A *circle* swoop, and a quick parabola under the bridge arches

Where light pushes through;

A sudden turning upon itself of a thing in the air.

A dip to the water.”

—D.H. (David Herbert)

“A man should not go where he cannot carry his whole sphere or society with him,Mnot bodily, the whole *circle* of his friends, but atmospherically. He should preserve in a new company the same attitude of mind and reality of relation, which his daily associates draw him to, else he is shorn of his best beams, and will be an orphan in the merriest club.”

—Ralph Waldo Emerson (1803–1882)