The trill (or shake, as it was known from the 16th until the 19th century) is a musical ornament consisting of a rapid alternation between two adjacent notes, usually a semitone or tone apart, which can be identified with the context of the trill. (compare mordent and tremolo). It is sometimes referred to by the German triller, the Italian trillo, the French trille or the Spanish trino. A cadential trill is a trill associated with a cadence.
A trill provides rhythmic interest, melodic interest, and—through dissonance—harmonic interest. Sometimes it is expected that the trill will end with a turn (by sounding the note below rather than the note above the principal note, immediately before the last sounding of the principal note), or some other variation. Such variations are often marked with a few appoggiaturas following the note that bears the trill indication.