TAO is the "x" or unknown quantity that we have to find.

And the first thing to be done is to see what is predicated of this mysterious Thing; how it is described; with what attributes it is credited; where it is to be found; whence it sprang, how it exists, and what its functions are. Then we may find ourselves in a position to discover what it is that answers to these particulars, and profanely to give a name to that which its preachers themselves declared must be for ever nameless.