Biking is a gear heavy sport, all the way down to the shoes. And different types of biking have different styles of shoes and cleats when you're riding clipless pedals. The jargon is odd too, I know, but biking becomes more efficient when you wear a biking shoe that clips into a pedal. This way you can power your pedaling during the full circle of a pedal stroke. One type of cleat/pedal combination is SPD, which stands for Shimano Pedaling Dynamics — Shimano being a manufacturer of bicycle gear. SPD pedals have recessed cleats so you can walk around normally if need be, which is why they are favored by mountain bikers, but many road bikers use them too. When riding in urban areas, SPD cleats work well too, since un-clipping frequently can be necessary with traffic lights. Since the cleat is recessed you actually get traction on the ground, which is handy. However, since the cleat is pretty small, foot pain while biking can be an issue, since you're putting the pressure of your foot repeatedly onto a small surface area.