Good catch, and your guess was close! "Wind Booster" is the old Korean name for the Buccaneer's Speed Infusion, not a Wind Archer skill. This book would raise Speed Infusion to master level 30, but in this version Speed Infusion only goes up to 20. So the book was never finished: it has no picture, no description and does nothing. The real game never drops it. A few monsters (Ghost Pirates and others) were still dropping it here because of an old drop list. That's removed, so it no longer drops anywhere. The working Speed Infusion book (raises it to 20) still drops as before. The one you already have does nothing, so feel free to sell it or drop it.