What is Pennon?

Legal Definition
A pennon or pennant is a flag that is larger at the hoist than at the fly. It can have several shapes, such as triangular, tapering or triangular and swallow-tailed.

It was one of the principal three varieties of flags carried during the Middle Ages (the other two were the banner and the standard). Pennoncells and streamers or pendants are minor varieties of this style of flag. The pennon is a flag resembling the guidon in shape, but only half the size. It does not contain any coat of arms, but only crests, mottos and heraldic and ornamental devices.
-- Wikipedia
Legal Definition
A standard, banner or ensign carried in wav.
-- Black's Law Dictionary