Meaning
A bold letter B in a square, usually red, made to label blood type B. It doubles as a plain capital B or a B grade.
Besides blood types and grades, it has a well-known meme use: swapping random letters, especially B or P, for 🅱️ to make words sound silly: “Let’s get this 🅱️read” It also marks plan B or option B in polls. Pair it with 🅰️ for comparisons.