Sway back is the hips pushed forward of the ankles with the upper body leaning back to balance.
The person hangs in the front of the hips; the chest and head go backward so the mass stays over the feet. In 📝Postural / Structural Realignment it is a hanging strategy, often with a long 📝posterior chain and a tucked or dumped pelvis, not a diagnosis of a spinal condition. The useful question is whether the hips can also sit back over the heels without the chest throwing itself rearward.
Clients feel it as locking the knees and hanging. Cueing is weight into the whole foot, a quieter hip, and a stack they can keep without leaning. Pain or unsteadiness is a stop.
This is pattern language, not a structural correction.