Generally the difference is the bend point / flex point. Low flex point shafts would be designated as higher trajectory shafts and high flex point shafts would be lower trajectory shafts. There are other factors and the shaft companies are not always specific in how they make the determination, but overall I think you will find the bend point / flex point is what designates the trajectory profile. We publish what trajectory profile the shaft companies say they are. Important to note that even though a shaft may be designated a low or mid or high trajectory, the player and how they swing, etc. may produce a different trajectory results. A proper driver fitting is the best way to dial in the right shaft, loft combination to produce the optimum trajectory and spin for any given player.