Serialism is a broad category of compositional techniques that use rows of some musical elements, such as pitch or note duration or rhythm in which such elements are arranged so that each is played in a sequence selected by the composer.
In the case of pitch, for example, one note from each pitch class is contained in each row. Although notes can have different durations and different dynamics and fall on different beats, every note is included, thus pushing the work away from tonality. Although serial music is not necessarily atonal, it is closely associated with it.
The concept of serialism can be difficult for many music lovers to comprehend (just as music produced using serialism can be difficult for many music lovers to comprehend – and truly enjoy), and even amongst composers themselves there is much disagreement regarding the exact meaning of the term. But it is generally agreed that the term applies to all twelve-tone music. Twelve-tone composition is a specific type of serialism that deals with the orderings of the twelve pitches of the octave.
A major criticism of serialism is that, although the compositional technique itself may be interesting, the resulting sound is often incompatible with the way music is processed by the human brain, and thus many or most people enjoy such music far less than they enjoy music created by conventional techniques.