"Toxic" is a song by American recording artist Britney Spears, co-written and produced by Bloodshy & Avant, from her fourth album, In the Zone. It was released on January 12, 2004, by Jive Records as the second single from the album. After trying to choose between "(I Got That) Boom Boom" and "Outrageous" to be the second single from In the Zone, Spears selected "Toxic" instead. A dance-pop song with electropop influences, "Toxic" features varied instrumentation, such as drums, synthesizers and surf guitar. It is accompanied by high-pitched Bollywood strings and breathy vocals. Its lyrics refer to being addicted to a lover. The song has received critical acclaim by music critics, who deemed it as the strongest track of In the Zone, while praising its hook and chorus.

"Toxic" attained worldwide success, reaching the top-five in fifteen countries, while topping the charts in Australia, Canada, Hungary, Norway and the United Kingdom. In the United States, it became her fourth top ten single. The accompanying music video for the song was directed by Joseph Kahn and features references to Blade Runner, The Seven Year Itch and the films of John Woo. It portrays Spears as a secret agent in the search of a vial of green liquid. After she steals it, she enters an apartment and poisons her unfaithful boyfriend. The video also includes interspersed scenes of Spears naked with diamonds over her body. After Janet Jackson's Superbowl incident, the video was considered too racy for MTV and was moved to late-night programming.

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:

In music, a song is a composition for voice or voices, performed by singing. A song may be accompanied by musical instruments, or it may be unaccompanied, as in the case of a cappella songs. The lyrics (words) of songs are typically of a poetic, rhyming nature, though they may be religious verses or free prose.

A song may be for a solo singer, a duet, trio, or larger ensemble involving more voices. Songs with more than one voice to a part are considered choral works. Songs can be broadly divided into many different forms, depending on the criteria used. One division is between "art songs", "pop songs", and "folk songs". Other common methods of classification are by purpose (sacred vs secular), by style (dance, ballad, Lied, etc.), or by time of origin (Renaissance, Contemporary, etc.).

A song is a piece of music for accompanied or unaccompanied voice or voices or, "the act or art of singing," but the term is generally not used for large vocal forms including opera and oratorio. However, the term is, "often found in various figurative and transferred sense (e.g. for the lyrical second subject of a sonata...)." The noun "song" has the same etymological root as the verb "to sing" and the Oxford English Dictionary (OED) defines the word to mean "that which is sung" or "a musical composition suggestive of song." The OED also defines the word to mean "a poem" or "the musical phrases uttered by some birds, whales, and insects, typically forming a recognizable and repeated sequence and used chiefly for territorial defence or for attracting mates."