What defines a 'Trill' in music?

A 'Trill' is a musical ornament that involves rapidly alternating between a written note and the note immediately above it in pitch. This embellishment creates a vibrant, expressive sound, adding flair to the music. The distinguishing feature of a trill is specifically this alternating pattern, which emphasizes the written note while introducing a sense of motion and excitement through the rapid shifts.

The selected choice accurately captures the essence of a trill, showcasing the connection between the written note and the note above it, which is technically correct. It reinforces the trill’s primary function in performance practice as a tool for ornamentation and expression.