If you picture a large, heavy wooden door on a church from the middle ages in Europe, you might picture some large metal objects embedded in the wood. They are similar to the huge "nails" or "spikes" that attach the hinges to the door. Those might also be called studs.

 If you picture a man �s dress shirt, sometimes they don �t have buttons down the front. Instead, they have a series of holes down the front, and the man has a set of objects that fit into these holes and serve the purpose of buttons. These are also called studs. I think you can see that these two objects are somewhat similar (although shirt studs are much smaller, of course)