In music, syncopation includes a variety of rhythms which are in some way unexpected in that they deviate from the strict succession of regularly spaced strong and weak beats in a meter (pulse). These include a stress on a normally unstressed beat or a rest where one would normally be stressed. "If a part of the measure that is usually unstressed is accented, the rhythm is considered to be syncopated."
Syncopation is used in many musical styles, if not all, and is fundamental in such styles as funk, ska, reggae, ragtime, rap, jump blues, progressive rock, jazz and often in dubstep, heavy metal, and classical music. "All dance music makes use of [syncopation] and it's often a vital element that helps tie the whole track together". In the form of a back beat, syncopation is used in virtually all contemporary popular music.
Syncopation can also occur when an strong harmony is placed on a weak beat, for instance when a 7th-chord is placed on the second beat of 3/4 measure or a dominant is placed at the fourth beat of a 4/4 measure. The latter frequently occurs in tonal cadences in 18th and early 19th century music and is the usual conclusion of any section. A hemiola can also be seen as one straight measure in 3 with one long chord and one short chord and a syncope in the measure therafter, with one short chord and one long chord: 3 ≥ . | . ≥ | Usually, the last chord in a hemiola is a (bi-)dominant, and as such a strong harmony on a weak beat, hence a syncope.