The centre of mass is the point where weight is considered to act

Moments, Couples & Equilibrium — AQA A-Level Physics

Key Definition

Centre of mass — The point at which the entire weight of an object may be considered to act.

For a uniform regular object, the centre of mass is at its geometric centre (point of symmetry).
The centre of mass can lie outside the physical body (e.g. a ring or L-shaped object).
A human's centre of mass shifts depending on posture: lower when leaning forward, higher when standing upright.