Yep, the key thing here is the temperature:
Dry hopping involves adding hops to the FV (or sometimes the keg) after fermentation. When the beer is cool, it doesn't drive off the delicate aroma - this is the ultimate for getting hop aroma. Its even possible to dry hop using an in-line hop container between the keg and beer tap for even fresher hop aroma. But the lack of heat also means theres not a great deal of flavour and hardly any bitterness extracted. (It also helps to wait until after the fermentation, because the C02 being created and floating away can (as I understand it) carry off aroma with it).
Hops that are added whilst the boiler is at 100c have much more aroma driven off but the heat helps to extract more bitterness and flavour. Those boiled for a long time also have flavour driven off too, so mostly just add bitterness (60 or 90mins hops), but later ones (say 20, 15, 10 and 0 min hops) contribute progressively more flavour and less bitterness. 0 min can sometimes be called 'flame out' as its when you switch/turn off the boiler, this is perhaps the soonest you could consider the hops to be technically called post-boil but theres not a massive difference to those added slightly earlier.
Sort of sitting between the two is the 80c steep - if you add hops below 80C (as the boiler cools) theres supposedly now not enough heat to extract much bitterness or to drive off as much aroma as when its hotter. Personally I used this extensively and it works but I'm moving away from it because I find it a bit of a compromise, and seem to get better results (especially for aroma) from different combinations of later boil and dry hops to get the ballance of flavour and aroma I want.
Just to complicate matters there is also First Wort Hopping, which is rather open to debate but you add them to the boiler as its filled - the theory is that the hot but not yet boiling wort causes a conversion which allows flavour to make it through the boil, at the expense of some bitterness. I've experimented with this and believe it does do something like that, but currently I'm finding it more predictable to separate bittering and flavour in terms of 90min and later hops.
All that aside though, to some extent we can struggle to perceive flavour and aroma as separate things, so its all enormously subjective.
Cheers
kev
