A simple upward arrow, but on Twitter/X and Reddit it doubles as shorthand agreement — replying with just ⬆️ under a comment means "what they said" or "this," pointing up at the previous message. It's part of the original arrow set from Unicode's earliest emoji days (based on Japanese carrier pictographs), designed for compass/map directions long before it became internet agreement-speak.
Keywords: arrow, cardinal, direction, north, up