Final answer:
The flag when it is folded into a triangle is commonly known as a folded flag, traditionally used in the United States for military funerals, symbolizing the tri-corner hat worn during the American Revolution.
Step-by-step explanation:
The flag when it is folded into a triangle is commonly known as a folded flag or a less commonly as a burial flag. This style of folding the flag is traditionally used in the United States during the ceremonial folding and presentation of the flag at military funerals, where the blue field and stars are displayed on the outside. The triangle shape symbolizes the tri-corner hat worn by the patriots of the American Revolution, adding deeper historical meaning to the act.