Spur gears certainly are a type of cylindrical gear, with planetary gearbox shafts that are parallel and coplanar, and teeth that are directly and oriented parallel to the shafts. They’re arguably the simplest and most common kind of gear – simple to manufacture and suitable for an array of applications.
The teeth of a spur gear have an involute profile and mesh one tooth at the same time. The involute form implies that spur gears only generate radial forces (no axial forces), however the method of tooth meshing causes high pressure on the gear teeth and high noise creation. For this reason, spur gears are typically used for lower rate applications, although they can be utilized at almost any speed.