Meaning
A solid square, usually inside a button, the stop control on media players. Unlike pause, it ends playback completely and resets to the start.
In chat it is a firm “stop” or “enough”, used to end a debate, a running joke or a bad habit: “No more spoilers please ⏹️” Pair it with ✋ or 🙅 for emphasis. If you only need a short break, ⏸️ is softer and less final.