Engine and Transmission Tech

Somewhat of a newb question, but I am about to get a set of heads ported and have read many threads on this and other boards that refer to Stage 2, 3 and 4 porting and preparation. I have looked on several web sites - John Eales, V8 tuner and others and they seem to use different terms.
Is there a generally accepted definition associated with each term - I am not expecting that there is an ISO type classification, but would love to get a better understanding before I embark on my project. In a post from last year Dan Jones and a couple of others were referring to Stage 3 and Stage 4 level work done on stock 4.6/4.0 heads and I would love to understand what that meant and whether it was transferable.

Thanks very much for any enlightenment or any links to posts that would answer the question.

Nick

IMHO, This defers to how much cash flow, you are willing to hemorage. Without specific description of work and flowbench reports, for each level of spending, what are you really getting ? Porting is like swimming from shore. The further-out you go, the easier, to get lost. Good Luck, roverman.