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:

“That three times five is equal to the half of thirty, expresses a relation between these numbers. Propositions of this kind are discoverable by the mere operation of thought, without dependence on what is any where existent in the universe. Though there never were a *circle* or triangle in nature, the truths, demonstrated by Euclid, would for ever retain their certainty and evidence.”

—David Hume (1711–1776)

“Every few years something new breaks into the *circle* of my thoughts.”

—Mason Cooley (b. 1927)

“There is all the difference in the world between departure from recognised rules by one who has learned to obey them, and neglect of them through want of training or want of skill or want of understanding. Before you can be eccentric you must know where the *circle* is.”

—Ellen Terry (1847–1928)