“Maya” is another word for “samsara”, or “phenomenal world”. It is a Sanskrit word that basically means “illusion”.
The whole of our world is maya. Not only our sensory, physical world but also the whole psychical world, that is the world of emotion/desire and thought. Why is it called illusory has to be explained, for it is not that obvious. It does indeed seem very real. Here are 3 basic ideas:
First, it is a world of relativity: meaning everything that is to be found in our physical and psychical world exists relatively to a multiplicity of other things. In other words, nothing exists by itself, nothing is self-existing. Life forms, objects, phenomenons of all kinds are the result of a multiplicity of concurring factors, elements, occurrences that make those temporary things what they are. In and of themselves, they are not. They are illusory in the sense that they contain no actual truth, only relative truth.
Second, forms, physical, or psychical are all is in a constant state of change, from one moment to the next, and are all going towards their inevitable disappearance. An illusion is a fleeting, fluctuating thing. It seems to exist but is just an appearance, soon to vanish. “Soon” is itself a relative concept, for even a million years is soon, if compared to infinity.
Third, we must grasp the idea that the multiple temporary forms that our world is made of, are the fluctuating illusion. The fundamental energy, or matter (physical or psychical) that these forms are made of, is real. It is said that energy cannot be created nor destroyed. This is a corresponding idea. Our world is an illusion, but the “stuff” or basic energy our world is made of, is real.