Tao can be translated as "path" or "the way", in the sense of the force which flows through all life and is the first cause of everything.

Some meanings from here and there:

The Tao is formless.
The Tao exists since the beginning.
The Tao has no beginning and ending.
The Tao is "The Way" or "The Law", "The Rule".
The Tao is "Something" which exists behind all of process in the universe.
Everything can happen because there is a "Law", because there is a "Rule", because there is a "Way".
Everything can happen because of "The Tao".

"Tao is the course, the flow, the drift, or the process of nature," says Alan Watts in Tao: The Watercourse Way (1975). While in other cultures light opposes darkness, good opposes evil, life opposes death, each one struggling to eliminate the other, in the Tao both light and darkness, good and evil, positive and negative are essential for the continuation of life. Opposites are seen as the two edges of one and the same pole, as north and south: you cannot have the one without the other. The two poles of cosmic energy-yang, positive, active, male, and yin, negative, passive, female-are essential for harmonious balance. (lefthandofdarkness.html)

"... people tend to think that the Way is some kind of path, or that it referes to the way of doing things or some sort of direction that we take. But the Tao is everything. Each of us is the Way; each of us is walking the Way."

Infinite Circle Bernie Glassman