flag

(countable)A piece of cloth, often decorated with an emblem, used as a visual signal or symbol.

(countable, uncountable)The design that could be placed on a flag, typically a rectangular graphic that is used to represent an entity (like a country, organisation or group of people) or an idea.

The flag of France has three vertical stripes.

(countable, uncountable)(nautical) A flag flown by a ship to show the presence on board of the admiral; the admiral himself, or his flagship.

(attributive, countable, often, uncountable)(nautical, often used attributively) A signal flag.

(countable, uncountable)The use of a flag, especially to indicate the start of a race or other event.

(countable, uncountable)(computer science) A variable or memory location that stores a Boolean true-or-false, yes-or-no value, typically either recording the fact that a certain event has occurred or requesting that a certain optional action take place.

(countable, uncountable)(computer science) In a command line interface, a command parameter requesting optional behavior or otherwise modifying the action of the command being invoked.

(countable, uncountable)(aviation) A mechanical indicator that pops up to draw the pilot's attention to a problem or malfunction.

(British, uncountable)The game of capture the flag.

(countable, uncountable)(geometry) A sequence of faces of a given polytope, one of each dimension up to that of the polytope (formally, though in practice not always explicitly, including the null face and the polytope itself), such that each face in the sequence is part of the next-higher dimension face.

(countable, uncountable)(mathematics, linear algebra) A sequence of subspaces of a vector space, beginning with the null space and ending with the vector space itself, such that each member of the sequence (until the last) is a proper subspace of the next.

(countable, uncountable)(television) A dark piece of material that can be mounted on a stand to block or shape the light.

To furnish or deck out with flags.

To mark with a flag, especially to indicate the importance of something.

(often, with down)(often with down) To signal to, especially to stop a passing vehicle etc.

Please flag down a taxi for me.

To convey (a message) by means of flag signals.

to flag an order to troops or vessels at a distance

(often, with up)(often with up) To note, mark or point out for attention.

I've flagged up the need for further investigation into this.

Users of the Internet forum can flag others' posts as inappropriate.

(computing) To signal (an event).

The compiler flagged three errors.

(computing) To set a program variable to true.

Flag the debug option before running the program.

To decoy (game) by waving a flag, handkerchief, etc. to arouse the animal's curiosity.

(sports) To penalize for an infraction.

The defender was flagged for unsportsmanlike conduct.

(intransitive)(chess, intransitive) To lose on time, especially in a blitz game; when using a traditional analog chess clock, a flag would fall when time expired.

Mark Dvoretsky (2014), For Friends & Colleagues, volume 1, →ISBN: “Indeed, I usually spent an hour to an hour and a half on my game, never found myself in time pressure, never once flagged in my entire life, except in blitz games, of course.”

(transitive)(chess, transitive) To defeat (an opponent) on time, especially in a blitz game.

White was winning positionally, but Black managed to flag him and win.

(firearms) To point the muzzle of a firearm at a person or object one does not intend to fire on.