In physics, the word system has a technical meaning, namely, it is the portion of the physical universe chosen for analysis. Everything outside the system is known as the environment, which in analysis is ignored except for its effects on the system. The cut between system and the world is a free choice, generally made to simplify the analysis as much as possible. An isolated system is one which has negligible interaction with its environment.

Often a system in this sense is chosen to correspond to the more usual meaning of system, such as a particular machine. But physical systems are often more esoteric: an atom, the water in a lake, or indeed the water in the left-hand half of a lake can all be considered as physical systems. In the study of quantum decoherence the "system" may refer to the macroscopic properties of an object (e.g. the position of a pendulum bob), while the relevant "environment" may be the internal degrees of freedom, described classically by the pendulum's thermal vibrations.

System of a Down, also known by the acronym SOAD and often shortened to System, is a rock band from Southern California, formed in 1994. It consists of Serj Tankian (lead vocals, keyboards, rhythm guitar), Daron Malakian (guitar, vocals), Shavo Odadjian (bass, background vocals) and John Dolmayan (drums).

The band achieved commercial success with the release of five studio albums; from which three debuted at number one on the Billboard 200. System of a Down has been nominated for four Grammy Awards, and won the award in 2006 for Best Hard Rock Performance for the song "B.Y.O.B.". The group went on hiatus in August 2006, but reunited in November 2010, embarking on a worldwide tour in 2011.

Serj Tankian, Daron Malakian, and Shavo Odadjian all attended Rose and Alex Pilibos Armenian School while children, although because of their eight-year age difference they did not meet until 1992 while working on separate projects at the same recording studio. They formed a band named Soil with Tankian on vocals and keyboards, Malakian on vocals and guitar, Dave Hakopyan (who later played in The Apex Theory/Mt. Helium) on bass and Domingo "Dingo" Laranio on drums. The band hired Shavo Odadjian (another Rose and Alex Pilibos alumnus) as manager, although he eventually joined Soil as rhythm guitarist. After three years, only one live show, and one jam session recording, Hakopyan and Laranio quit the band, feeling that it was not going anywhere.