Factory stance is the position of the inserts. Stance setback is the measure thatlet's us know how far back the center between the inserts (bindings) is from the center of the effective edge of the snowboard.
Centered stance (or centered factory stance / centered inserts / no setback) Better for freestyle because it helps a snowboard to ride switch as well as it rides forward, gives you good control in both directions and makes the snowboard turn easily. Found in most freestyle snowboards, in some all mountains, and in very few or none freeride/powder snowboards. Also found in all snowboards named true twin, in lots of snowboards named directional twin, or twin like, and in very few (or none) snowboards named directional.
Small stance setback (or small factory stance setback / small inserts setback) Good for all mountain and great for freeride/powder because it makes the tail smaller (so it naturally sinks in deeper snow conditions) and the nose bigger (which makes it float better in the same deeper snow conditions). small stance setback (about 25mm/1inch) may be found in some freeride/powder snowboards, in some all mountains, and in a few freestyle snowboards. Also found in some boards described as directional snowboards, in lots of snowboards described as directional twin, and not in any snowboard called true twin. The tail will feel stiffer, giving you more aggreesive direction changes and higher ollies, and it will float a bit better when riding powder.
A bigger stance setback may be found in lots of freeride/powder snowboards, in some all mountains, and in very few or none freestyle snowboards. Also found in lots of boards described as directional snowboards, in few or none snowboards described as directional twin, and in no snowboard called true twin. The tail will feel even stiffer, giving you even more aggressive direction changes and on powder will float like a charm with more centered and relaxed riding position.
Such a huge stance set-back can only be found in snowboards described as "freeride/powder boards" and "directional snowboards". The word here is buoyancy!
Powder inserts / extra inserts
Two extra inserts that allow you transform your freestyle or all-mountain snowboard into a powder board when you most need one, and then go back to your more centered stance when you don't. These two inserts stand alone at the back of the other inserts, separated from them. Big binding discs (universal discs) will attach to the last two inserts and to the two powder inserts the same way they would in a board with 2x2 inserts. They work as 2x2 inserts (not the standard 4x2) and are not compatible with mini-disc bindings. Powder inserts are more common in all-mountain snowboards.