Meaning
A solid red square from the emoji version 12.0 colour set. It means red and works as a building block for pixel art, grids and colour codes.
Football fans use it as a red card, and people build progress bars, heat maps and tiny pixel drawings with it: “Straight 🟥 in the first half, unbelievable” It also flags errors or stopped tasks in status lists. The round version is 🔴.