The Rogan is an abbreviation of the "ROyal groGAN". It applies to a grogan of complete and absolute perfection in all categories of analysis. The rogan is very rare, and if in a lifetime you lay 2 or 3 of these great creations, you have led a successfull existence.
There is much debate as to whether one can lay a perfect (or royal) grogette but still not create a rogan. My personal belief is that a royal grogette does not immediately imply a rogan.
The Shogan is an abbreviation for a "SHithouse grOGAN". This is a grogan that is so poor (in either length, viscosity, smell or voraciousness) that upon being laid in the crapper, it is rejected by it, and consequently will not flush down.