What term describes the style of performing music in a humorous or joking manner?

The term that describes the style of performing music in a humorous or joking manner is "giocoso." This Italian word translates to "jovial" or "playful" in English. When musicians see "giocoso" in the score, they understand that the piece should be played with light-hearted spirit and a sense of fun, allowing for expressive freedom and a whimsical character.

The other terms, while relevant in music, refer to different concepts. "Severe" indicates a more serious or solemn style of performance, which contrasts sharply with the playful connotations of "giocoso." "Allegro," meaning fast and lively, focuses on the tempo rather than the emotional tone of humor. Lastly, "forte" describes a loud volume and does not imply anything about the mood or character of the performance. Hence, "giocoso" is the correct term for a humorous style of music.