It can only be 'defined' in negative terms, ie; that which it is not. Since it is incomprehensible via the rational mind, it cannot be defined, because to define it is to encapsulate it somehow. The Tao, being infinite and eternal, cannot be so encapsulated.
What you call 'the real world' is effervescent and temporal. It has no absolute existence, so how can you call it 'real'?
The word Tao has several meanings and many applications. Primarily, Tao refers to the eternal, life-giving force of the universe. Tao is the universe. It is also the process by which the universe governs itself. It is all-inclusive. There is nothing outside Tao. It is, in Lao Tzus words, the mother of all things. Everything that takes form is an expression of the Tao. All of us are the Tao - you, me, people on the other side of the world, Christians, Muslims, atheists, plants, animals, rocks, air, good guys, bad guys all one, all part of one whole.
Beneath the apparent separateness of the ten thousand things of everyday life is a deeper underlying unity.
A more contemporary way of stating this is that all life is a never-ending net or sea of energy. Tao is that energy, life-giving and benevolent....
Mystery The Art of Not-Knowing
The opening lines of the Tao Te Ching state, The Tao that can be told is not the true Tao. The name that can be named is not the true name. Names, while useful, can be limiting. We must go beyond names and see the Tao in all things. In the same opening chapter Lao Tzu writes that to fully experience Tao one must enter its mystery, a mystery shrouded in darkness, darkness within darkness. To do so we are required to go beyond our traditional ways of thinking and perceiving, and beyond a traditional understanding of knowing itself.
Conventional knowledge is based on making distinctions and determinations, on gathering information. It is the realm of our rationality. However, this level of mind simply cannot encompass the vastness of life. Rationality is limited in the way it perceives. Our intuitive understanding, on the other hand, is connected to universal wisdom, to the Tao, and speaks our deepest truths. This understanding is experiential rather than intellectual. We become that understanding.
Chuang Tzu encourages us let go into not-knowing. When we stand in awe of the sunset we are not analyzing how it sets. We simply take in the experience. Our mind is calm, quiet, and empty, and we are fully present. We can also learn to bring the same letting go, the same simply being, to all areas of life, including those involving change or conflict. We learn to trust that whatever information is necessary to bring balance to a given situation is present in the Tao. And as part of the Tao, that information is available to us if we are open and receptive. Our rational mind can then apply that information in a skillful manner.
Whether we are appreciating natures work or facing some challenge in the world of human affairs, we can allow ourselves to experience and appreciate the mystery. Not fearing the unknown, we can enter the mystery, and from that darkness within darkness will emerge the order and balance that is characteristic of the movement of the Tao.
Taoist Sanctuary: Ageless Wisdom for a Modern World