• Flap (aircraft), a hinged surface on the trailing edge of an airplane wing
• Flapping, one of the basic mechanics of flight in birds
• Flap, any hinged plate often used as a cover or a simple one-way valve
• Cat flap, a hinged flap that allows a cat to enter or leave a room or building
• Butt flap, a separately removable part of underwear (un)covering the buttocks
• Sluice or flap gate, a pressure driven water flow control device between a channel and other water body
• Flap consonant, a sound produced by brief contact between the tongue and the roof of the mouth
• Intervocalic alveolar flapping, a process by which a /t/ phoneme] before an unstressed vowel is pronounced as a flap consonant
• Free flap, a surgical transfer of vascularised tissue
• Flap (Little Nemo), a minor character from Little Nemo: Adventures in Slumberland
• Route flapping, when a router alternately advertises a destination network first via one route then another
• Brouhaha, a general state of social agitation
• 5-lipoxygenase activating protein (FLAP)
• Flap (JumpStart 4th Grade), a purple vampire bat from JumpStart Adventures 4th Grade: Haunted Island

See also

• Flapper, a woman who wore a certain style of clothes in the 1920s
• Flapping races, unlicensed horse rains in the UK and Ireland