"Horizontal" is an idea which requires a preferred direction in space. That happens on the surface of a planet because the interaction between the solid surface and the local gravity provides that preferred direction.

Most of the universe does not have a "horizontal" and experiences

• orbital motion in all planes (though not all at the same frequency own), and for circular orbits this is uniform. The orbits of human deployed satellites are often nearly circular and run in many different planes.
• rotational motion in all planes and for stable rotations this is uniform. The rotations of the planets of our solar system point in a bunch of funny directions.

The free rotation of uniform bodies can proceed at any angle from the horizonatal because the gravitational forces balance out. Think of a spinning wheel.

Driven rotation can approach arbitrarily close to uniformity is the driving force far exceed the unbalanced gravitational forces.

An aside that started life as a comment but grew a bit out of hand.

"Horizontal" is an idea which requires a preferred direction in space. That happens on the surface of a planet because the interaction between the solid surface and the local gravity provides that preferred direction.

Most of the universe does not have a "horizontal" and experiences

• orbital motion in all planes (though not all at the same frequency own), and for circular orbits this is uniform. The orbits of human deployed satellites are often nearly circular and run in many different planes.
• rotational motion in all planes and for stable rotations this is uniform. The rotations of the planets of our solar system point in a bunch of funny directions.