STD is indeed for Standard. That's the relatively recent change from the "bars" proof pressure marks used by the British proof houses since the mid to late 80's. What it means, to me, is--with 2 3/4" chambers--I would stick with standard US target ammo (skeet loads), 3/4 oz, 1200 fps. I wouldn't go with any heavier shot charges or any higher velocity stuff like the hotter sporting clays loads, which are in the 1300 fps range. Just to be on the safe side.