Lower on the jacket, there are the hip pockets. The hip pocket construction varies, and reflects formality, style, and function. The simplest form of hip pocket in construction is sewn onto the outside of a suit jacket using matching fabric. We call this, a patch pocket. Commonly found on workwear, hunting, and safari jackets, patch pockets can feature a flap and button for added security.
Jetted pockets, instead, are pouches inside the garment with a slit opening, giving a sleek appearance suitable for formal wear. The design likely originated with Edward VII's tailors when the King requested a silk-lined jacket. There, the tailors noticed that pouches can easily be hidden between the main fabric, canvassing, and inner lining.
Another theory is that jetted pockets with a flap were meant to protect contents inside the pocket from rain and weather, with the flap tucked inside the pocket when indoors. The effect is a cleaner, flatter look. Flapped jetted pockets are a very common and versatile design choice. The flap can be hidden inside the pocket to create a slit opening, which is often suggestive of more formal occasions.