This word has several distinct uses based on its geometrical shape: Mathematical: A three dimensional triangular shape with a meeting of the angles at the apex. Archaeological: Egyptian, Mayan and Inca pyramids. The most famous pyramid is the Great Pyramid of Cheops. Organizational: A pyramid structure is a hierarchical organization more people in lower positions and fewer in senior positions above them. Pyramid schemes: Schemes where a few people sell bogus entitlements to larger numbers for rewards. 
Examples of Pyramid:
Their management structure is a classic pyramid. This is just pyramid selling, not real business. The pyramid is a common feature of several ancient cultures. http://faculty.plattsburgh.edu/richard.robbins/legacy/population_readings.htm http://en.wikipedia.org/wiki/Population http://en.wikipedia.org/wiki/World_population 
Pyramid of khafra 
The 1skeleton of pyramid is a wheel graph 
