Syncopation is a musical term meaning a variety of rhythms played together to make a piece of music, making part or all of a tune or piece of music off-beat. More simply, syncopation is "a disturbance or interruption of the regular flow of rhythm": a "placement of rhythmic stresses or accents where they wouldn't normally occur".[1] It is the correlation of at least two sets of time intervals.[2]

Syncopation (sfz) in Beethoven's String Quartet in A major, Op. 18, No. 5, 3rd movement, mm. 24–25
Vertical hemiola (the ratio 3:2)

Syncopation is used in many musical styles, especially dance music. According to music producer Rick Snoman, "All dance music makes use of syncopation, and it's often a vital element that helps tie the whole track together".[3] In the form of a back beat, syncopation is used in virtually all contemporary popular music.[citation needed]

Syncopation can also occur when a strong harmony is simultaneous with a weak beat, for instance, when a 7th-chord is played on the second beat of 3
measure or a dominant chord is played at the fourth beat of a 4
measure. The latter occurs frequently in tonal cadences for 18th- and early-19th-century music and is the usual conclusion of any section.

A hemiola (the equivalent Latin term is sesquialtera) can also be considered as one straight measure in three with one long chord and one short chord and a syncope in the measure thereafter, with one short chord and one long chord. Usually, the last chord in a hemiola is a (bi-)dominant, and as such a strong harmony on a weak beat, hence a syncope.