The phrase "extra flap" means having more than what is needed or necessary. It refers to having additional things or actions that are not required or useful. Full definition
«The coats I found were plain and unflattering, cumbersome, with extra flaps, panels, zippers and snaps. (mamanloupsden.com)
Rinse scallops with cold water and remove any of the side muscles (the little extra flap found on the side of the scallops) that are present. (peasandcrayons.com)
The Miracle Blanket has a hard - to - kick - out - of foot pouch and extra flaps for securing tucking your baby's arms down, so it really does resemble a straitjacket. (alphamom.com)