a line enclosing a plane areas
"The gardener walked along the perimeter to ensure every edge of the garden was fenced in."
the size of something as given by the distance around it
"The security team spent hours measuring the perimeter of the large warehouse to ensure no gaps existed in the fence line."
The sum of the distance of all the lengths of the sides of an object.
"The perimeter of the rectangular garden is forty feet, calculated by adding together the length of each side."
In plain English: Perimeter is the total distance around the outside edge of any shape.
"The gardener measured the perimeter of the flower bed to decide how much fencing she needed."
Usage: Use perimeter specifically to describe the total length around a two-dimensional shape, whereas circumference refers exclusively to circles and spheres. Do not use this term for the boundary line itself; that is simply called the edge or border.
The word perimeter comes from the Latin perimetros, which was borrowed directly from Ancient Greek. It originally combined elements meaning "around" and "measure," reflecting its core concept of measuring a boundary.