The symbol known as the enneagram is apparently a recent addition, at least as far as published references are concerned.
It is first mentioned in the writing of spiritual teacher P.D. Ouspensky  who attributes it to the teachings of G.I. Gurdjieff , another well known spiritual teacher of modern times.  It is in the form of a circle with a triangle and other shapes inside resulting in nine points on the circle and is a variation of the nanogram.  The triangle formed by points 3, 6 and 9 are said to represent the physical universe.  The points 1,4,2,8,5, and 7 represent the spiritual dimensions or worlds of light.  The number seven is seen a lot in spiritual writings.  According to many of the ancient mystery schools, the perfect Light from heaven is a seven-fold light.  We see that also in Malachi's description of the Sun of Righteousness.  So this symbol represents on one level, the relationship and the ongoing conflict between the material and the spiritual.  
    Today, another use of this symbol has evolved in which it is knows as the Enneagram of Personality.  It is believed by it's followers that by answering some basic questions, we can all be divided into 9 primary personality types represented by the points on the enneagram.  You can take a test of you personality type (a short one that's free or a longer one with a fee) at this web site.