Tao (the way or path) is a concept central to the ancient Chinese philosophy of Taoism.
Taoism is an outlook on life that attempts to harmonize the individual will with natural and spiritual influences. Personal thoughts and actions alternately coincide or conflict with the Tao, which signifies the flow of the universe, or in some commentaries, the Will of Heaven.
Ideally, ones lives in wu-wei, which has been translated as “effortless action.” This does not imply inaction, per se. The Taoist can be quite active. But again, this action is in line with the Tao.
One of the classic passages oft quoted about the Tao comes from Lao Tzu, who says
I do not know its name; I call it Tao.
In other words, Lao Tzu realizes that naming the Tao always falls short of its true meaning.¹
¹ More here: http://en.wikiquote.org/wiki/Laozi