It literally translates to "of good humor", but it's more commonly used to describe someone's general emotional state.
Here are some examples of how you might use it:
* "Estoy de buen humor hoy." (I'm in a good mood today.)
* "Ella siempre está de buen humor." (She's always in a good mood.)
* "Él no está de buen humor." (He's not in a good mood.)
Let me know if you have any other questions! 😊