The center of mass, referred to as the center of mass for short, refers to an imaginary point on the material system where mass is concentrated. Unlike the center of gravity, the center of mass does not have to be in a system with a gravitational field. It is worth noting that unless the gravity field is uniform, the center of mass and the center of gravity of the same material system are usually not on the same imaginary point.
The centroid of a surface is the geometric center of a cross-sectional figure. Centroid is used for real objects, and centroid is used for abstract geometry. For real objects with uniform density, the centroid and centroid coincide.