Rhythm is the duration of time that the note is sounded or a variation of the length and accentuation of a series of sounds or other events. Standard music notation contains rhythmic information and is adapted specifically for drums and percussion instruments. The drums are generally used to keep other instruments in ‘time’. They do this by supplying beats/strikes in time at a certain pace, i.e. 70 beats per minute (bpm). In Rock music, a drum beat is used to keep a bass/guitar line in time. In Western music, rhythms are usually arranged with respect to a time signature, partially signifying a meter. The speed of the underlying pulse is sometimes called the beat. The tempo is a measure of how quickly the pulse repeats.
The tempo is usually measured in ‘beats per minute’ (bpm); 60 bpm means a speed of one beat per second. The length of the meter, or metric unit (usually corresponding with measure length), is usually grouped into either two or three beats, being called duple meter and triple meter, respectively. If each beat is divided by two or four, it is simple meter, if by three (or six) compound meter. According to Pierre Boulez, beat structures beyond four are “simply not natural”. His reference is to western European music.
Syncopated rhythms are rhythms that accent parts of the beat not already stressed by counting. Playing simultaneous rhythms in more than one time signature is called polymeter or polyrhythm.