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. Flags can be of different kinds and used for different purposes.
A national flag is a flag that represents and symbolizes a given nation. It is flown by the government of that nation, but usually can also be flown by its citizens.
Maritime flags are predominately used at sea to to communicate with and between ships. Various navies have flag systems with additional flags and codes.
Because flags can signal and identity, they are often used in sports.
Some flags are used to represent or identify certain groups within the community or can be used as a symbol of expression.