What is the difference between a bittering hop, flavor hops, and aroma hops?

Answer 1

In the past there was a theory that certain hops should only be used for bittering/flavor and aroma hops.  Certain professional and home brewers no longer adhere to this past theory.  Currently some brewers consider the difference in terms of when the hops are added to the boil.  Bittering hops are added early in the boil, flavor hops are added during the middle and towards the end, whereas aroma hops are added at the very end of the boil, after flame out and sometimes during fermenting (also known as dry hopping).  The bittering hops counter the sweetness of the malt, flavoring hop add hop character to the beer and aroma hops add to the wonderful bouquet of the finished beer.