Flaps are flexible surfaces on an aircraft's wings or tail that can be moved to change the airflow and lift. They are primarily used during takeoff and landing to increase lift at lower speeds, allowing the aircraft to fly safely at slower velocities. In addition to aircraft, flaps can also be found in other contexts, such as in book covers that have flaps to protect the pages or in envelopes that have flaps to seal the contents inside. These flaps serve practical purposes, enhancing functionality and safety in various applications.