What term in music signifies a stressed note?

The term that signifies a stressed note in music is "accent." An accent indicates that a specific note should be played with greater emphasis or loudness compared to the surrounding notes. This allows composers and performers to convey emotion and add nuance to their music, making certain parts stand out. Accents can enhance the rhythmic and dynamic qualities of a piece, guiding musicians on how to interpret the score.

The other terms listed do not pertain to stressing a note. "Ritardando" refers to a gradual slowing down of the tempo, affecting the overall pace rather than emphasizing specific notes. "Alla" is typically part of phrases like "alla breve," which indicates a specific time signature. "Ad libitum" denotes the freedom to perform a passage at one's discretion, allowing for personal interpretation but not specifically relating to the concept of emphasis on a note.