The three-volley salute is a ceremonial act performed at military funerals and sometimes also police funerals. The custom likely originates with Roman funeral rites. Dirt would be cast on the body three times followed, and the ceremony was ended by the deceased's name being called three times. It was then customary for the friends and relatives of the deceased to repeat the word 'vale' (meaning farewell or goodbye) three times. In more recent history three volleys were fired to signify the end of a funeral and that the burial detail was to be ready for battle.[1]
It should not be confused with the 21-gun salute (or 19-gun or 17-gun, etc.) which is fired by a battery of artillery pieces.