The whole thought of Laozi is developed around the central concept of Dao  However, the 73 characters of Dao in Laozi have different meanings although the symbol form is unified
Metaphysical noumenon
 In some places, Dao refers to the origin of the existence of the world, in some places, Tao refers to a law, and in some places, Dao refers to a standard of life, which reflects the unified outlook on life of Dao