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
A rule of life
 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