An important idea that Advaitins believe very strongly in is the concept of : Brahma Satya, Jagat Mithya -- the World is an Illusion, Consciousness is the Only Reality. This idea rests on three other concepts namely that of the Atman -- the Self, the Brahman -- the Supreme Consciousness and the elusive concept of Maya -- the Illusion. These three crucial concepts can be summarized as follows1 :
Atman - the Self : The entire phenomenal world is bound by time, space and causation and as long as one is confined by these concepts, the experience is limited. Beyond the realms of time and space, there is an absolute and unconditional Reality that has no beginning and no end. That is Atman, the Self. The Self cannot be experienced by the senses. This Self is both within and outside the body. Unlike the body it is beyond death and decay. The Self is the fountainhead of the life force that animates and motivates the mind-body complex. According to Sankara, this Self is the all-pervading, self-illumined Consciousness.
Brahman - the Supreme Consciousness : Brahman is the ultimate Truth within and without. Brahman is also all-pervading and self-illumined Consciousness and the relationship of the Brahman to the Self is that of the forest to the tree. The entire universe emanates from Brahman, exists in Brahman and at the time of dissolution returns into Brahman. Stepping beyond the primitive monotheism of the Judeo-Christian philosophy/theology, Sankara asserts that the individual Atman and the universal Brahman are one and the same and the concept of a creator that is distinct from the creation is a cosmic illusion.
Maya - the Illusion : The phenomenal universe that can be perceived by the senses is actually an illusion called Maya. This Maya is what causes human beings to perceive worldly phenomena and respond to the environment. Vedanta states that Maya shields the Truth or Brahman from the Self or Atman. The concepts of time and space that veil the face of Truth are aspects of Maya. Because Maya veils the Truth, the individual Atman misconstrues both the world and itself as different from the Truth or Brahman.