The [associahedron][1] or Stasheff polytope.

 [![alt text][2]][2]  
<sub>(source: [wikimedia.org](https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Polytope_K3.svg/180px-Polytope_K3.svg.png))</sub>  


  [1]: http://en.wikipedia.org/wiki/Associahedron
  [2]: https://i.sstatic.net/J3Nie.png