Center of mass

The point at which the mass of a rigid body can be considered to be concentrated.  More technically, it is the point from which the sum of the moments of inertia of all parts of the body is zero.  The centre of mass is not always located in the body as it is dependent of posture for its location (see figure below).

The centre of mass (●) is located in the body when it is the vertical position (A), but falls out the body when one leans forward (B)

See Biomechanics, Center of gravity, Inertia, Mass, Moment of inertia (I), Newtonian (or classical) mechanics, Newton’s law of universal gravitation, Posture, Postural control