Sexual orientation is an enduring pattern of romantic or sexual attraction (or a combination of these) to persons of the opposite sex or gender, the same sex or gender, or to both sexes or more than one gender. These attractions are generally subsumed under heterosexuality, homosexuality, and bisexuality, while asexuality (the lack of sexual attraction to others) is sometimes identified as the fourth category.
These categories are aspects of the more nuanced nature of sexual identity and terminology. For example, people may use other labels, such as pansexual or polysexual, or none at all. According to the American Psychological Association, sexual orientation "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". Androphilia and gynephilia are terms used in behavioral science to describe sexual orientation as an alternative to a gender binary conceptualization. Androphilia describes sexual attraction to masculinity; gynephilia describes the sexual attraction to femininity. The term sexual preference largely overlaps with sexual orientation, but is generally distinguished in psychological research. A person who identifies as bisexual, for example, may sexually prefer one sex over the other. Sexual preference may also suggest a degree of voluntary choice, whereas sexual orientation is not a choice.
Scientists do not know the exact cause of sexual orientation, but they theorize that it is caused by a complex interplay of genetic, hormonal, and environmental influences. Although no single theory on the cause of sexual orientation has yet gained widespread support, scientists favor biologically based theories. There is considerably more evidence supporting nonsocial, biological causes of sexual orientation than social ones, especially for males. There is no substantive evidence which suggests parenting or early childhood experiences play a role with regard to sexual orientation. Across cultures, most people are heterosexual, with a minority of people having a homosexual or bisexual orientation.: 8 : 9–10 A person's sexual orientation can be anywhere on a continuum, from exclusive attraction to the opposite sex to exclusive attraction to the same sex.
Sexual orientation is studied primarily within biology, neuroscience, and psychology (including sexology), but it is also a subject area in sociology, history (including social constructionist perspectives), and law.