Music is the art of arranging sound. It is one of the universal cultural aspects of all human societies. Music may be defined with styles that emphasize, de-emphasize, or omit common elements of organized sound, such as rhythm, volume and pitch. Rhythm may be specified with tempos, sometimes organized using meters, and often coordinating the variation and juxtaposition of pitch. Individual sounds possess timbres or texture, which heavily contribute to the music's overall character.
The relationships and divisions between genres are inexact and sometimes hotly contested, as in taxonomy. The mere existence or legitimacy of a genre may be a topic of controversy. It is sometimes more valuable to categorize music by era, scene, intent, or artistic inspiration. Individual periods of music are separated into pieces, which can be categorized into numerous traditions, such as songs, tracks, symphonies, or so forth. Pieces may be composed and performed using a vast range of instruments, including the human voice. There are solely instrumental pieces, solely vocal pieces, pieces that combine singing and instruments, pieces with no sound, randomly generated pieces, and even pieces merely specifying an environment with no further sonic organization.
In some musical contexts, a performance or composition may be to some extent improvised. For instance, in Hindustani classical music, the performer plays spontaneously while following a partially defined structure and using characteristic motifs. In modal jazz the performers may take turns leading and responding, while sharing a changing set of notes. In a free jazz context, there may be no structure whatsoever, with each performer acting at their discretion. Music may be deliberately composed to be unperformable, or agglomerated electronically from many performances. Music is played in public and private areas, highlighted at events such as festivals, rock concerts, and orchestra performance, and heard incidentally as part of a score or soundtrack to a film, TV show, opera, or video game. Musical playback is the primary function of an MP3 player or CD player and a universal feature of radios and smartphones.
Music often plays a key role in social activities (such as dancing, karaoke singing, and attending concerts), religious rituals, rite of passage ceremonies, graduation and marriage celebrations, and cultural activities such as community choirs. It can be a hobby or a profession, like a teen playing cello in a youth orchestra or a local funk band hired for parties. The music industry includes songwriters, performers (including orchestra, jazz band and rock band musicians, singers and conductors), sound engineers, producers, tour organizers, distributors of instruments, accessories, and sheet music. Compositions, performances, and recordings are assessed and evaluated by music critics, music journalists, and music scholars, as well as amateurs. Like visual art and literature, music is widely created, appreciated, academically studied and criticized, and has been for thousands of years.