I mentioned this formation in another post. It's when DT is lined up in shotgun and has two backs beside him and one about two yards behind him...sort of forms an "A"
I'm not a big fan of it because it allows defenses to tighten up versus spread out... It would seem to me going to 4 receiver sets and leaving a back would force the defense to spread out more and still give you a running option. When we ran it against Tulane we saw waves of defenders coming in and making plays behind the line of scrimmage.
I guess the positive is that it leaves a lot of backs to block against a pass rush...gives you more options to run the ball.
I'm not a football coach so feel free to educate me otherwise.