Heterosexuality is romantic attraction, sexual attraction or sexual behavior between persons of the opposite sex or gender. As a sexual orientation, heterosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" to persons of the opposite sex; it "also refers to a person's sense of identity based on those attractions, related behaviors, and membership in a community of others who share those attractions."
Along with bisexuality and homosexuality, heterosexuality is one of the three main categories of sexual orientation within the heterosexual–homosexual continuum. Someone who is heterosexual is commonly referred to as straight.
The term heterosexual or heterosexuality is usually applied to humans, but heterosexual behavior is observed in all mammals and in other animals.
Hetero- comes from the Greek word έτερος [héteros], meaning "other party" or "another", used in science as a prefix meaning "different"; and the Latin word for sex (that is, characteristic sex or sexual differentiation). The term "heterosexual" was first published in 1892 in C.G. Chaddock's translation of Krafft-Ebing's "Psychopathia Sexualis". The noun came into use from the early 1920s, but did not enter common use until the 1960s. The colloquial shortening "hetero" is attested from 1933. The abstract noun "heterosexuality" is first recorded in 1900. The word "heterosexual" was first listed in Merriam-Webster's New International Dictionary as a medical term for "morbid sexual passion for one of the opposite sex"; however, in 1934 in their Second Edition Unabridged it is defined as a "manifestation of sexual passion for one of the opposite sex; normal sexuality". The adjective heterosexual is used for intimate relationships or sexual relations between male and female.