A 56 degree is a sand wedge.
The 54 is a sand wedge, SWs have a higher bounce to get the ball out of sand easier.
The standard wedge has a 46° loft. The "Grass-N-Sand" variant has a 50° loft.
I carry a Lob wedge in my bag and it is a 60 degree loft club. It is one of 4 wedges that I carry. The others are a Pitching wedge which is 45 degree, a Gap wedge which is 51 degree, and a Sand wedge which is 56 degree.
The "D" is for Dual. It's a dual wedge w/ a 50 degree between pitching wedge and sand wedge.
the sand wedge for this set is 55 degrees
56 degree loft