Plato's Cave is an allegory from the ancient Greek philosopher Plato. It is used to explain the nature of reality and how we perceive it. The allegory is based on a group of people who have been chained in a cave since birth, facing a blank wall.
From Wikipedia
Plato was an ancient Greek philosopher of Classical Athens who is most commonly considered the foundational thinker of the Western philosophical tradition. An innovator of the literary dialogue and dialectic forms, Plato influenced all the major areas of theoretical philosophy and practical philosophy, and was the founder of the Academy, a philosophical school in Athens where Plato taught the collection of philosophical theories that would later become known as Platonism.