system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Is the solar system rotating on the same horizontal level or are they rotating in different positions in a 3D sphere around the sun?
gpt
Most of the stuff is rotating in roughly the same plane around the sun. Though there are a ton of small objects, principally in very long orbits, that rotate at other angles as well.

The stuff that all rotates in the same plane does so because of conservation of angular momentum. Basically, they all started off from the same big, rotating cloud of dust that formed the solar system. They were all rotating in different directions. However, as objects traveling around the center of mass of the cloud (where the sun is now) in different directions collided, some of this rotational motion was cancelled out. If you were to "average out" the direction of rotation about the center of the cloud, that's the direction most things revolve around the sun travel. Since motion orthogonal (at a right angle to) this direction all got "canceled out," most of the solar system rests on a plane. 

The objects that don't rotate on that plane are mostly objects the solar system has pulled in after it formed or are just a portion of the few, small objects that didn't collide with much stuff in the early days of the solar system and happened to retain their odd angle of rotation about the sun.