Maya

Maya is the process of superimposition by which worldly objects are perceived in the omnipresent Brahm. It is a result of Avidya (ignorance). When one gets liberated, Maya is vanished.

To understand this, consider the process of mirage, when water is perceived in the desert. Another example often used in Vedantic literature is that of a man looking at a rope and thinking of it as a snake.

What we see around us (this world) is not an absolute reality, but a perception by the five senses.

You can argue that even if what you are seeing is an illusion, how come every one also sees the same illusion! How come both you and your friend see exactly the same room, the same chair and the same colors, if they are not real? The short answer is that even your friend (and all that he/she is saying and thinking) is just in your mind.