While some authors define "circumference" as distance around an arbitrary closed object (sometimes restricted to a closed curved object), in the work, the term "perimeter" is used for this purpose and "circumference" is restricted to mean the perimeter of a circle.
or 
,
 |
where 
is pi.
The term "circumference" is also sometimes used to refer to the "enclosing boundary" itself of a curved lamina or disk.
