How is the perimeter of a circle commonly referred to?

The perimeter of a circle is commonly referred to as its circumference. This term specifically describes the total distance around the circle. The circumference can be calculated using the formula (C = 2\pi r) or (C = \pi d), where (r) represents the radius and (d) represents the diameter of the circle.

The other terms listed are related to circles but have different meanings. The area refers to the space enclosed within a circle, measured in square units. The radius is the distance from the center of the circle to any point on its edge, while the diameter is the distance across the circle through the center, equal to twice the radius. These distinct definitions help clarify that circumference specifically pertains to the outer boundary or "perimeter" of the circle.