A two-dimensional planar closed surface which has a mass and a surface density (in units of mass per areas squared) such that

The center of mass of a lamina is called its geometric centroid.

A two-dimensional planar closed surface which has a mass and a surface density (in units of mass per areas squared) such that

The center of mass of a lamina is called its geometric centroid.

Weisstein, Eric W. "Lamina." From *MathWorld*--A
Wolfram Web Resource. https://mathworld.wolfram.com/Lamina.html