Alpha Capo

Taken from a Bass fishing Forum and pretty good explanation:

Much of the confusion has to do with terminology. Let's define "power" and "action" first.

Power
The power of a rod is simply a rating, which describes the overall stiffness of the blank. Power categories include Ultra-Light (UL), Light(L), Medium-Light(ML), Medium(M), Medium-Heavy(MH) , Heavy(H) and Extra Heavy(XH)

Action
The action of a rod is a rating, which describes the amount of curvature that occurs in the blank due to loading with weight. The faster the action, the further towards the tip the rod bends. The slower the action, the further towards the middle of the rod and so on.

Action categories include:
Extra-Fast: Bend very near the top of the blank.
Fast: Bend in the upper 25-30%.
Moderate: Bend near the middle.
Slow: Parabolic curvature throughout the entire length of the rod.

Action is important because it determines, in part, how much control you have over the fish. The faster the action, the more pressure you can put on the fish (and vice-versa). Many crankbait anglers want more moderate action so that the fish cannot shake free as easily. Another important consideration of rod action is casting distance. The slower the action the better the rod will cast. Rods that have a slower action have a wider curve on their parabolic bend, and therefore can store more potential energy when casting. This is called "rod loading." In effect, the more the rod loads, the more of the rod you use to cast. Fast action rods bend closer to the tip, using less of the rod to cast.

Other rod characteristics to note are recovery, sensitivity and brittleness. Recovery is a measure of the time it takes the rod to recover after a cast. When you impart energy to a rod upon casting, it vibrates. You can see the tip shaking. That shaking bats the line as it leaves the top guide, causing friction. That friction reduces casting distance. Faster action rods tend to recover faster, but do not load up as well. More moderate action rods tend to recover poorly, but load up better. If you can find a moderate action rod with fast recovery, it will outcast everything else if the rest of the playing field is equal.

Sensitivity is obviously important. You want a rod to be able to transmit the feelings you experience when your lure moves underwater, where you can't see it. Higher modulus graphite is more sensitive, although it may be a case of diminishing returns as you get higher and higher up the modulus rating scale.

Brittleness is how easily the rod will break. Most high end rods are brittle, as brittleness and sensitivity tend to be indirectly proportional. That's where a lifetime warranty comes into play!

So, all things are not created equal and if you think a $50 rod is just as good as a $300 rod, you're wrong! Buy the best equipment you can afford and focus on quality, not quantity.

For an all around rod I recommend 6 1/2' or 7' Medium Power/ Fast Action. More than 90% of all the bass fishing you will ever do can be done with this rod. Rod power is more about the weight of the lures you use than the fish you might catch. A Medium Power rod will handle most of the lures you will fish and the fight will be much more fun.

Now for the details. I'll list the Power and Action and a specific rod:

If I were to fish one rod only: 7" M/F spinning. G.Loomis GLX PR844S

If I can fish two, my other rod would be: 7' H/F baitcasting. G.Loomis GLX MBR844C

For technique specific applications:

Light fishing: 6 1/2' ML/F spinning
Soft plastics: 7' M/F spinning
Crankbaits, jerkbaits and topwater: 7' M or MH/M baitcasting
Spinnerbaits and buzzbaits: 7' M or MH/F baitcasting
Jigs, C-rigs and heavy and/or deep running lures: 7' H/F baitcasting

And to break it down just a little further, I fish a Heavy Power/ Slow Action glass rod for big, treble hook lures.