Many natural phenomena cannot be explained if Earth were flat, including the observation that the bottom part of a distant object appears clipped. To “explain” it as if it can occur on a flat Earth, flat-Earthers invented the “explanation” that it is due to what they call “perspective.”
This supposed “perspective” that flat Earthers invented is different from the actual law of perspective. To distinguish it from the actual, real-world law of perspective, many people call it “flerspective,” a combination of the words flerf and perspective.