Which term describes a musical element where the strong and weak beats within a measure are changed?

The term that describes changing the strong and weak beats within a measure is syncopation. Syncopation involves placing emphasis or accents on normally weak beats or using rests on strong beats, which creates a feeling of rhythmic surprise and tension. This technique adds variety and interest to the music, often leading to a more dynamic and compelling rhythmic experience. It is commonly used in various musical genres, including jazz, funk, and even classical music, to break away from predictable rhythmic patterns.

In contrast, relative timing refers more broadly to the timing relationships between notes, while accentuation pertains to emphasizing certain notes or beats without specifically altering their position as strong or weak in the measure. Ritardando is a tempo term that indicates a gradual slowing down of the music, unrelated to the treatment of strong and weak beats.