Meaning
A plain black flag waving on a pole. Black flags have been used for mourning, protest and pirate imagery, among other things, so its meaning depends heavily on context.
People use it for dark or edgy aesthetics, team colours and all-black outfits: “Team Black, assemble 🏴 dress code all black” Technically it is also the base character for the flags of England, Scotland and Wales and for 🏴☠️, which are built by adding hidden codes to it.