In music, what's the term for a rapid alternation between two adjacent notes?
And the answer: trill.
In printed music, a trill is seen above a note with either the letters tr, or with a plus sign. This is a signal to the musician to play the note, and then rapidly go back and forth between the printed note and the note above it.
Also known as embellishments or flourishes, musical ornaments are added to decorate melodic lines. Most ornaments are performed as "fast notes" around a central note, and can vary widely in number depending on the composer or musical epoch. Baroque music, for one, is a style and period in music history that is characterized by extensive ornamentation. While most of these extraneous notes were improvised, Bach was the first composer to begin recording them on sheet music. Others, such as Handel, Vivaldi and Corelli, followed suit (or should we say suite?).
Aside from the trill, there are many other forms of musical ornamentation. A mordent, for one, is similar to a trill in execution but consists of a single or a few alternations rather than many. Meanwhile, an appoggiatura comes from the Italian verb appoggiare, meaning "to lean upon," and is a note placed on the beat before a regular note. There are also acciaccaturas (grace notes), turns, glissandos, and more.
Learn more about musical ornamentation below.