A placket is simply a slit in a blazer, shirt, skirt or jacket. It can also be a pocket. Sometimes new apparel has a stitch holding the slit together and that is referred to as a placket as well. When you get an item with the big X-shape, that is a temporary stitch binding the placket. Those are the ones you should remove so your garment flows nicely and you can have the freedom to move easily in it. That’s it, remove the placket.