[TexasGator]

"Action refers to how quickly a rod returns to “straight” from a “bent” (curved) position, not how flexible or heavy duty it is."

It returns more quickly because the rod isn't bent as far.

[Paul R.]

There is more to it than that. You can have a light duty rod that is “fast action” but still bends a lot with a big fish on - if it doesn’t snap, that is. “Action” is actually a function of taper design, AND mechanical resistance (damping / internal friction), AND flexibility (spring constant.)