(idiomatic, simile) Extremely quickly.

(meteorology, astronomy) A very rare phenomenon observed in the morning or evening when the sun is crossing or immediately below the horizon, in which a momentary flash of blue light appears above the upper rim of the solar disk, caused by refraction of light in the atmosphere.

(countable) A fictional story that is briefer than typical short stories. / (uncountable) The genre of such stories.

In video or film editing, a very short shot (usually one frame, but occasionally several) appearing in a sequence of images. Flash frames are usually the inadvertent result of an editing mistake or an equipment problem. From time to time, however, they are inserted intentionally for creative reasons.

plural of flash fiction

Taking photographs using a camera with a flash.

Someone who participates in a flash mob.

plural of flash cut

(idiomatic) To recall or remember something; to experience a flashback.

(of a memory or vision) To move forward in time.