The trailing edge of the wing is the part that is referred to as the flaps.
circular
The flaps are simply called flaps.
winglett
Flaps generally change the geometry of the wing for landing and take off speeds
winglett
the wing flaps go up and down
That would be the flaps. There are flaps on the trailing edge of a wing on most aircraft and there can also be leading edge flaps as well, often seen on the big airliners. These flaps will be lowered and will effectively increase the curvature of the wing, allowing it fly at higher angles of attack for greater lift. It also produces greater drag, useful for dropping altitude without speeding up and flying slow on approach to landing.
The wing is the main flying surface. Control surfaces include the ailerons, flaps and slats.
To reduce the drag
Flaps in some cases are used to increase wing surface area. In most small single and multi-engine airplanes the flaps that are being utilitized usually plain, split or slotted, do not increase the surface area. They increase the camber (camber being the distance between the mean thickness of the wing and the line going from the leading edge to the trailing edge (called the chordline)), and also increase the coefficient of lift (or how hard the wing is working to produce lift). On most transport category airplanes they utilize what is called fowler flaps. These flaps increase the surface area of the wing by moving the flaps rearward on a track. This rearward movement increases those things stated earlier and also increased the surface area, which also produces more lift.
The cantle and the sweat flaps
Extending the wing flaps increases the wing surface area, which can increase lift at lower speeds by creating more lift-producing air pressure. However, the increased surface area also increases drag by creating more drag-inducing air resistance. Overall, extending wing flaps is a trade-off between increasing lift for lower speeds and increasing drag, which can impact fuel efficiency and performance.