The term perimeter refers either to the curve constituting the boundary of a lamina or else to the length of this boundary.
The perimeter of a circle is called the circumference, although that term is used by some authors to refer to the perimeter of an arbitrary curved geometric figure.
The perimeter of a region is implemented in the Wolfram Language as Perimeter[reg].
The perimeters of some common laminae are summarized in the table below. In the table, 
is the eccentricity of an ellipse, 
is its semimajor axis, and 
is a complete
elliptic integral of the second kind.
