any broad thin and limber covering attached at one edge; hangs loose or projects freely
"he wrote on the flap of the envelope"
the motion made by flapping up and down
"The wings beat rapidly to generate lift as the bird hovered in place."
a movable piece of tissue partly connected to the body
"The surgeon carefully inspected the flap before suturing it into place."
Anything broad and flexible that hangs loose, or that is attached by one side or end and is easily moved.
"The old curtain flapped gently in the breeze, swinging freely from its top rod."
In plain English: A flap is a loose piece of material that hangs down and can move around easily.
"The baby threw his arms and legs in an excited flap while playing on the floor."
Usage: As a noun, flap refers to any piece of material like fabric or leather that hangs loosely from an opening, such as the cover on a suitcase pocket. When used as a verb, it describes the action of moving this type of flexible object rapidly back and forth.
pronounce with a flap, of alveolar sounds
"The Spanish word for water is pronounced with a distinct alveolar flap sound in the middle."
To move (something broad and loose) up and down.
"The wind caused his jacket to flap wildly against his legs as he ran through the field."
In plain English: To flap is to move your arms, wings, or other body parts up and down quickly while flying or swimming.
"The little bird flapped its wings to take off from the branch."
The word "flap" comes from Middle English, where it originally meant a slap or blow as well as something flexible like an open wing. It traveled into modern usage through these older Germanic roots that described both striking actions and loose movements.