What is this "wave" for?
It's something to assist opening. First used by the Emerson company in their knives, though they don't really make that many compared to other companies. When properly pulled from the pocket, the hook catches the corner or lip of the pocket and the blade opens as a result. Note that this is a good way to mess up a decent pair of slacks and even my jeans show accelerated signs of wear (though mine are good quality so it's not an issue, more a reminder to not overuse it). Getting it out more slowly or at a different angle bypasses this for times you actually like your pants.