flag, flagpole, flagstaff
Always lowercase:
the United States flag
May be called a banner, a standard, or the colors.
Ensign, streamer, pennant, and jack are special kinds of flags.
Capitalize Old Glory, Maple Leaf, Tricolor, and Union Jack.
A flagpole is a permanent fixture; it carries a flag.
A flagstaff is borne by a person, ship, or vehicle
A flagstaff carries the colors (a flag borne by a person, ship, or vehicle).