A national flag is a flag that represents and symbolizes a given nation. It is flown by the government of that nation, but can also be flown by its citizens. A national flag is typically designed with specific meanings for its colours and symbols, which may also be used separately from the flag as a symbol of the nation. The design of a national flag is sometimes altered after the occurrence of important historical events. The burning or destruction of a national flag is a greatly symbolic act.

A flag is a piece of fabric with a distinctive design and colours. It is used as a symbol, a signalling device, or for decoration. The term flag is also used to refer to the graphic design employed, and flags have evolved into a general tool for rudimentary signalling and identification, especially in environments where communication is challenging. Many flags fall into groups of similar designs called flag families. The study of flags is known as "vexillology" from the Latin vexillum, meaning "flag" or "banner".