1 [no object] (of a light or something that reflects light) shine in a bright but brief, sudden, or intermittent way:the lights started flashing (as adjective flashing)a police car with a flashing light
[with object] cause to shine briefly or suddenly:the oncoming car flashed its lights
[with object] shine or show a light to send (a signal):red lights started to flash a warning
[with object] give (a swift or sudden look):Carrie flashed a glance in his direction [with two objects]:she flashed him a withering look
express a sudden burst of emotion, especially anger, with a swift or sudden look:she glared at him, her eyes flashing
2 [with object] display (an image, words, or information) suddenly on a television or computer screen or electronic sign, typically briefly or repeatedly:suddenly the screen flashes a message
[no object] (of an image or message) be displayed briefly or repeatedly on a screen:the election results flashed on the screen
informal hold up or show (something, often proof of one’s identity) quickly before replacing it:she opened her purse and flashed her ID card
informal make a conspicuous display of (something) so as to impress or attract attention:they all flash their money around
[no object] (often as noun flashing) informal (especially of a man) show one’s genitals briefly in public.
3 [no object] move or pass very quickly:a look of terror flashed across Kirov’s facethe scenery flashed byanother stray thought flashed through her mind
[with object] send (news or information) swiftly by means of telegraphy or telecommunications:the story was flashed around the world
1a sudden brief burst of bright light or a sudden glint from a reflective surface:the grenade exploded with a yellow flash of lighta lightning flash
2a thing that occurs suddenly and within a brief period of time, in particular.
a sudden instance or manifestation of a quality, understanding, or humor:she had a flash of inspiration
a news flash.
3 (Flash) Computing, trademark a platform for producing and displaying animation and video in web browsers.
4a camera attachment that produces a brief very bright light, used for taking photographs in poor light:an electronic flashif in any doubt, use flash [as modifier]:flash photography
5excess plastic or metal forced between facing surfaces as two halves of a mold close up, forming a thin projection on the finished object.
informal, chiefly British
1(of a thing) ostentatiously expensive, elaborate, or up to date:a flash new car
(of a person) superficially attractive because stylish and full of brash charm:he was carrying this money around and trying to be flash
2 archaic of or relating to thieves, prostitutes, or the underworld, especially their language.
flash in the pan
a thing or person whose sudden but brief success is not repeated or repeatable:our start to the season was just a flash in the pan
[with allusion to the priming of a firearm, the flash arising from an explosion of gunpowder from the pan within the lock]
in (or like) a flash
very quickly; immediately:she was out of the back door in a flash
(as) quick as a flash
(especially of a person’s response or reaction) very quickly:quick as a flash, he was at her side
(of a person’s thoughts or mind) briefly and suddenly recall a previous time or incident:her thoughts immediately flashed back to last night
make an electric circuit by sparking across a gap.
(of a fire) spread instantly across a gap because of intense heat.
Middle English (in the sense 'splash water about'): probably imitative; compare with flush1 and splash