Terrain glitch

A terrain glitch is a terrain bug where the terrain generator makes a mistake when generating this part of celestial body's surface.

Polar Glitch

This is the most usual type of terrain glitch. It occurs as a very strange terrain on the poles of celestial bodies, like Moho or Eve. It's most likely a mistake happening when terrain generator attaches height values to a sphere.

Terrain Breakage

As is shown in its name, this is a glitch that terrain cracks. It provides a "entrance" to the "inner" of celestial bodies. But unfortunately, when flying something(like a poor Kerbal) into it, system will destory it immediately as it's under the surface.