imagine you get the ability to teleport to another plane of existence. At that place everything is different from this plane. There is no matter and what your perceive with your senses is a totally different kind of information than in this plane of reality.
Then, somehow, you can get a landscape... a beautiful place that you are able to process into your brain still not adjusted that experience.
that's a planescape.
I wanted to call it planscape, but then it would be confused with the black island games.