A perimeter is a path that surrounds an area. The word comes from the Greek peri (around) and meter (measure). The term may be used either for the path or its length - it can be thought of as the length of the outline of a shape. The perimeter of a circular area is called its circumference.

Read more about Perimeter:  Practical Uses, Formulae, Polygons, Circumference of A Circle, Perception of Perimeter