power vs. action

a little help please. I know the power of a rod, UL, L, Heavy, but where does the action come in? fast action, medium-fast, moderate fast, moderate? is this the taper of the tip, thinner to stouter that allows for more finesse in casting, in feeling of a bite? I'm updating my rods and I'm finding out I'm a bit ignorant on this. thanks

Pike, yer not alone. Ive always been coin-fused myself at times about that topic. I hope to see a few responses so I can clarify for myself as well.

The Deetz

Noodle rods bend all the way down and have slow action
This adds more of a shock absorber effect that helps when using a light line

wow! had this totally backwards. thought a fast action had more of the "whipping" and bending. glad I cleared this one up.

with a fast action rod you can toss heavier lures/flies further with less effort and motion. 
a slower action will dampen a quick surge by a fish better protecting the tippet/line.
it is said that a faster action you can throw tighter loops but once you get the feel of a rod and timing down, you can throw pretty tight loops with med/fast to med rods also.

i find a fast or med/fast action, stiffer rod, will tire a fish out faster than a slow or medium action.
i also find it's easier to roll cast a med/fast than a slower action.
a fast action rod roll casts better with more line out.

of course this is my experience and opinion!!