Meaning
A round button with a dot in the centre, like a selected option in an on-screen form. It means chosen or selected, one choice out of several.
It is handy for polls and quick choices written as text, usually paired with ⚪ for the options not picked: “Dinner tonight: 🔘 hotpot ⚪ pizza ⚪ sushi” It also works as a neat bullet or a stylised button in bios. The name comes from old radios, where pressing one button popped the others out.