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Flash \Flash\, n.; pl. {Flashes}.
1. A sudden burst of light; a flood of light instantaneously
appearing and disappearing; a momentary blaze; as, a flash
of lightning.

2. A sudden and brilliant burst, as of wit or genius; a
momentary brightness or show.

The flash and outbreak of a fiery mind. --Shak.

No striking sentiment, no flash of fancy. --Wirt.

3. The time during which a flash is visible; an instant; a
very brief period.

The Persians and Macedonians had it for a flash.
--Bacon.

4. A preparation of capsicum, burnt sugar, etc., for coloring
and giving a fictitious strength to liquors.

5. a lamp for providing intense momentary light to take a
photograph; as, to take a picture without a flash.

Syn: flashbulb, photoflash, flash lamp, flashgun.
[WordNet 1.5]

6. Same as {flashlight}. [informal]
[PJC]

7. (Journalism) A short news item providing recently received
and usually preliminary information about an event that is
considered important enough to interrupt normal
broadcasting or other news delivery services; also called
a {news flash} or {bulletin}.
[PJC]

{Flash light}, or {Flashing light}, a kind of light shown by
lighthouses, produced by the revolution of reflectors, so
as to show a flash of light every few seconds, alternating
with periods of dimness. --Knight.

{Flash in the pan}, the flashing of the priming in the pan of
a flintlock musket without discharging the piece; hence,
sudden, spasmodic effort that accomplishes nothing.