The general definition of circumference is a line or external boundary of a closed curvilinear figure or object. The more common definition of circumference within mathematics is the measure of the outer boundary (commonly called the perimeter) of an elliptical area, especially a circular area. The letter "C" commonly denotes the length of a circle's circumference. The circumference of a sphere is defined as the length of any great circle on the sphere. A great circle is the circle on the surface of a sphere produced by a plane that passes through the center of the sphere.

One of the earliest references to circumference was by Heraclitus of Ephesos (535-475 b.c.) when he used the word "periphereia" to mean "The beginning and end join on the circumference of the circle." Circumference most likely is a combination of the Latin "circum" (around) and "ferre" (to carry) and a...