From Wiktionary, the free dictionary

• IPA^(key): /ˈflæpɪŋ/
• Rhymes: -æpɪŋ

flapping (not comparable)

1. that flaps or flap

   flapping sails

flapping (countable and uncountable, plural flappings)

1. An instance where one, or something, flaps.

   • 1970, Richard Carpenter, Catweazle, Harmondsworth: Puffin Books, page 24:

     The farmyard was dark and he tiptoed across it so that the turkeys wouldn't set up their gobbling and flapping.

2. (phonology) A phonological process found in many dialects of English, especially American English and Canadian English, by which intervocalic /t/ and /d/ surface as the alveolar flap [ɾ] before an unstressed syllable, so that words such as "metal" and "medal" are pronounced similarly or identically.
3. (computing, telecommunications) The situation where a resource, a network destination, etc., is advertised as being available and then unavailable (or available by different routes) in rapid succession.
4. (uncountable) The unlicensed racing of horses or greyhounds.

   • 2009, Mark Clapson, The Routledge Companion to Britain in the Twentieth Century, page 332:

     Greyhound racing had its origins in whippet racing, which was derived in turn from hare coursing. By the early twentieth century, however, a form of dog racing held in 'flapping tracks' was a common pastime in the wastelands near working-class areas of industrial cities.

   • 2016, Gerald Hammond, The Language of Horse Racing, page 81:

     Flapping is racing which is not licensed by the Jockey Club. […] Anyone found participating in, or even attending, flapping races is liable to be warned off.

   • 2016, David Matthews, Man Buys Dog:

     Flapping is the arse end of greyhound racing, the lowest of the low. Part sport, part fairground attraction, flapping is the bare-knuckle fighting of dog racing.

flapping

1. present participle and gerund of flap