noun
1. : any of certain flags flown to indicate the presence of an officer of high rank or of the holder of a high governmental office — used in the British navy and the United States Army; compare personal flag
2. : a flag flown to identify the headquarters of a major unit of the United States Army that does not have an organizational color or standard
3. : a flag indicative of the ownership of a vessel (as the house flag of a commercial ship or the private signal of a yacht)