A circle is a shape consisting of all points in a plane that are a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves in a plane so that its distance from a given point is constant. You can divide a circle into smaller portions. A part of a circle is called an arc, and an arc is named according to its angle. A circle is the set of all points at a specific distance from a given point in two dimensions. Concentric circles. Two or more circles that have the same centre, but different radii. Congruent circles. Two or more circles with the same radius, but different centres. Circle Properties The diameter of a circle is the longest chord of a circle. Equal chords and equal circles have equal circumference. The radius drawn perpendicular to the chord bisects the chord. Circles having different radius are similar. The chords that are equidistant from the centre are equal in length. Circles are still symbolically important today -they are often used to symbolize harmony and unity. For instance, take a look at the Olympic symbol. It has five interlocking rings of different colours, which represent the five major continents of the world united together in a spirit of healthy competition.