A "small solar system body" is a very tiny object in our solar system, like a little rock or piece of dust. They are much smaller than planets or moons, and there are lots and lots of them floating around in space! Some of them are even so small that they don't have a round shape - they are just big blobs.
Scientists study these small solar system bodies because they can help us learn more about the early history of our solar system. They can also give us clues about how things like comets and asteroids move around in space. Plus, they're just really interesting to look at!