Meaning
A solid black heart. Its meaning depends heavily on the crowd: dark humor, a gothic or minimalist aesthetic, edgy style, or a stylish way to say you love something that is black, like a cat or an outfit.
It is also used for grief and mourning, as a quiet way to show sorrow: “Rest easy, Grandpa 🖤” In other contexts it can mean affection with a moody or ironic twist. Because of that mourning association, using it casually on someone’s happy post might feel off, and older readers may see it as gloomy or even unkind.