Question

Why is not the term perimeter used instead of circumference?

Answer 1

Circumference is a special case of perimeter. Both describe the total length of the boundary of a two dimensional figure, but circumference specifically refers to the perimeter of a curved figure or arc. Therefore it only applies to circles, ovals, ellipses, arcs, etc.

Answer 2

Both words are used to talk about how long the boundary is of a 2D figure. Think of circumference as a special case of finding the perimeter. The term circumference refers to the perimeter of a figure without sides or something like a circle or arc.

So if we were to look at a rectangle and try to determine how long the boundary is we would use perimeter. On the other hand, if we have a circle we have no way to track how long each side is therefore we use circumference.