The term Flap refers to repeated and/or multiple sightings of UFOs involving multiple witnesses and generally involving a particular geographical location over a set period of time. A UFO Flap can last from weeks to a few years, but generally does not last longer than a few years. Occasionally the term Flap will be used to describe a similar set of sightings of paranormal or cryptozoological creatures, such as Bigfoot, Loch Ness Monster, Mothman or other beings.
Flaps are by their definition transitory. If an area is alleging paranormal phenomenon lasting longer that a few years then such place may be more properly described as a window area or even a hell mouth.
UFO Flaps - A Context for Scientific Study