Stance setback is how far back from the board's center the reference stance position sits, measured in millimeters. It shifts your weight toward the tail, helping the nose rise in soft snow—similar to leaning back in a canoe to keep the bow from diving.
A centered stance (0mm) is what you want for park riding or if you ride switch often, since most twin boards use this. A slight setback of 10–20mm adds a bit of directional feel while keeping things versatile for all-mountain riding. For freeride and powder-focused boards, look for 25–40mm of setback to improve float in softer snow. Anything over 40mm is built specifically for deep powder.
Match your setback to where and how you ride most. And when mounting bindings, use the reference stance holes—don't just center them on a setback board, or you'll defeat the purpose of the design.