Be aware that any more Shimano calls ALL of their pedals SPD. Pedals with a model number preceded by an A or M use recessed mountain SPD shoes and cleats. Examples are PD-A530 or PD-M440.

Pedals referred to as SPD-SL with a 4 numeric digit model number are road pedals that take a large non-recessed shoe cleat on road shoes. Example number is PD-6620. To add to the confusion there are also PD-R540 pedals which are SPD-SL road pedals. Cleats of SPD and SPD-SL pedals are not interchangeable and will not fit the same shoes generally speaking.

You can also run into SPD-R pedals on places like ebay. Discontinued pedals and unique cleats are used that do not fit other Shimano pedals. Shimano pedal designs, terminology and compatibility has varied over time and can be confusing.