The phrase "front flap" refers to the outermost part of something, often a cover or a piece that folds over the front of an object or book. Full definition
This sleeveless top has a square neck, wide band shoulder straps, front flap pockets, and an exposed rear zip. (qunel.com)
It comes with a strong front flap which is magnetic for added security. (babieslounge.com)
Complete with a narrow notch collar, an appearance of a two pocket front flap detail, and four velvet buttons residing on the bottom of each sleeve. (sophieandtrey.com)