Toxicity is the degree to which a substance can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell (cytotoxicity) or an organ such as the liver (hepatotoxicity). By extension, the word may be metaphorically used to describe toxic effects on larger and more complex groups, such as the family unit or society at large.

A central concept of toxicology is that effects are dose-dependent; even water can lead to water intoxication when taken in too many doses, whereas for even a very toxic substance such as snake venom there is a dose below which there is no detectable toxic effect. Toxicity is species-specific, lending cross-species analysis problematic. Newer paradigms and metrics are evolving to bypass animal testing, while maintaining the concept of toxicity endpoints.

There are generally three types of toxic entities; chemical, biological, and physical:

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.