Meaning
A large cloud covering most of the sun, with just a sliver of sunlight visible, showing mostly cloudy, overcast weather. It suggests the sun is there, just hidden for now.
It describes grey days, muted moods and plans that might still go ahead: “🌥️ but no rain yet, picnic is still on.” In the sun-and-cloud set it is the cloudiest, more overcast than ⛅ and 🌤️.