The pirouette compensation is cool new feature that compensates Yaw around Pitch or Roll angle.
In other words, if you are flying tilted forward and apply Yaw, your multi will sort of turn to which ever way you apply Yaw. With PiroComp the multi will continue in a straight line, keeping whatever bank angle you have, rotating it around the frame as you Yaw.
Default setting is On.
PiroComp is located in Configuration > Stabilization tab > Advanced tab