L ast time we talked about fly rods, various weights of rods and their purposes. Differences in fly rods go much further than the weights of the rods.
Price is certainly a consideration, but the one that gives fits to fly rodders is the action.
A n accepted definition of Action is defined as the relative resistance to bending as you move down the length of a particular fly rod. Fast Action rods tend to resist bending sooner than Slow Action rods. Thus Slow Action rods tend to be more whippy and will not cast as far as Fast action rods will cast. Fast Action rods tend to generate higher line speeds which make them easier to cast into the wind and for longer distances. Between the two extremes, there are Moderate Action rods.