U+23F9 · emoji since 2014
The stop button is a solid square, the icon for halting playback. It means stop, end it, and bring things to a full stop.
It marks ending a recording or a track, the control for that's enough, stop right there.
In texting, ⏹️ does not carry a widely used hidden or slang meaning, so you can usually take it at face value. People send it just as it looks, to add a little visual touch or set the mood of a message. Only a handful of emoji have a separate texting code, and ⏹️ is not really one of them.
Its official Unicode name is the Stop Button emoji. In everyday chat most people just call it the stop button emoji or describe what it shows. Copy and paste it from the button at the top of this page.
The ⏹️ leads off a short phrase, and the rest of the words are written in cipher, every letter disguised as another emoji. Tap decipher to reveal the whole line.
Or make your own cipher in the translator.