Center of gravity is the point around which body weight balances, usually just in front of the sacrum in standing.
When the hips push forward, the chest leans back, or the head lives ahead of the feet, that point has moved and the rest of the body is paying to keep it over the base. In 📝Postural / Structural Realignment the practitioner watches where the mass actually sits, not an ideal chart. A sway-back, a tucked pelvis, or a forward ribcage is a strategy for parking that center, not a bone out of place.
Clients feel it as "where I am heavy." Cueing is often to let the weight find the feet or the sit bones before stacking the rest. This is a gravity observation, not a biomechanical proof and not a medical finding.
Sudden unsteadiness or a fall is a referral, not a harder balance drill.