Flag

A flag is a piece of cloth hung from a pole for signalling (as in semaphore) or to identify the bearer, in this sense also called a standard. A national flag is one of the important official symbols of a nation. The study of flags is known as vexillology.

Some particularly famous or interesting flags are:

• The Union Jack, the national flag of the United Kingdom.
• The Dannebrog, the national flag of Denmark. Also the similar Nordic-cross flags of the other Nordic countries.
• The Stars and Stripes, the national flag of the United States.

See national flag for information on national flags of other countries.

Subdivisions of countries frequently have flags. Government agencies and educational or other private institutions also sometimes have flags. The United Nations has a flag. Europe also has a flag (see European flag).

A great many specialized flags are used to signal between ships or from ship to harbour in ship transport. An example is an entirely yellow flag, which means that the ship's crew is quarantined for an infectious disease.

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In computer science, a variable? that holds a true or false value (see Boolean algebra) is often called a flag.

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A flag can also be an indicator, as in a "red flag" (a sign that something is amiss).

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