Heterosexuality is romantic attraction, sexual attraction or sexual behavior between people of the opposite sex or gender. As a sexual orientation, heterosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" to people 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." Someone who is heterosexual is commonly referred to as straight.
A lesbian is a homosexual woman or girl. The word is also used for women in relation to their sexual identity or sexual behavior, regardless of sexual orientation, or as an adjective to characterize or associate nouns with female homosexuality or same-sex attraction. The concept of "lesbian" to differentiate women with a shared sexual orientation evolved in the 20th century. Throughout history, women have not had the same freedom or independence as men to pursue homosexual relationships, but neither have they met the same harsh punishment as gay men in some societies. Instead, lesbian relationships have often been regarded as harmless, unless a participant attempts to assert privileges traditionally enjoyed by men. As a result, little in history was documented to give an accurate description of how female homosexuality was expressed. When early sexologists in the late 19th century began to categorize and describe homosexual behavior, hampered by a lack of knowledge about homosexuality or women's sexuality, they distinguished lesbians as women who did not adhere to female gender roles. They classified them as mentally ill—a designation which has been reversed since the late 20th century in the global scientific community.
Sexology is the scientific study of human sexuality, including human sexual interests, behaviors, and functions. The term sexology does not generally refer to the non-scientific study of sexuality, such as social criticism.
Richard Freiherr von Krafft-Ebing was a German psychiatrist and author of the foundational work Psychopathia Sexualis (1886).
The field of psychology has extensively studied homosexuality as a human sexual orientation. The American Psychiatric Association listed homosexuality in the Diagnostic and Statistical Manual of Mental Disorders (DSM) in 1952, but that classification came under scrutiny in research funded by the National Institute of Mental Health. That research and subsequent studies consistently failed to produce any empirical or scientific basis for regarding homosexuality as anything other than a natural and normal sexual orientation that is a healthy and positive expression of human sexuality. As a result of this scientific research, the American Psychiatric Association declassified homosexuality as a mental disorder in 1973. Upon a thorough review of the scientific data, the American Psychological Association followed in 1975 and also called on all mental health professionals to take the lead in "removing the stigma of mental illness that has long been associated" with homosexuality. In 1993, the National Association of Social Workers adopted the same position as the American Psychiatric Association and the American Psychological Association, in recognition of scientific evidence. The World Health Organization, which listed homosexuality in the ICD-9 in 1977, removed homosexuality from the ICD-10 which was endorsed by the 43rd World Health Assembly on 17 May 1990.
Psychosexual disorder is a sexual problem that is psychological, rather than physiological in origin. "Psychosexual disorder" was a term used in Freudian psychology. The term of psychosexual disorder used by the TAF for homosexuality as a reason to ban the LGBT people from military service.
Homoeroticism is sexual attraction between members of the same sex, either male–male or female–female. The concept differs from the concept of homosexuality: it refers specifically to the desire itself, which can be temporary, whereas "homosexuality" implies a more permanent state of identity or sexual orientation. It has been depicted or manifested throughout the history of the visual arts and literature and can also be found in performative forms; from theatre to the theatricality of uniformed movements. According to the Oxford English Dictionary, it is "pertaining to or characterized by a tendency for erotic emotions to be centered on a person of the same sex; or pertaining to a homo-erotic person."
Terms used to describe homosexuality have gone through many changes since the emergence of the first terms in the mid-19th century. In English, some terms in widespread use have been sodomite, Achillean, Sapphic, Uranian, homophile, lesbian, gay, effeminate, queer, homoaffective, and same-gender attracted. Some of these words are specific to women, some to men, and some can be used of either. Gay people may also be identified under the umbrella terms LGBT.
The Well of Loneliness is a lesbian novel by British author Radclyffe Hall that was first published in 1928 by Jonathan Cape. It follows the life of Stephen Gordon, an Englishwoman from an upper-class family whose "sexual inversion" (homosexuality) is apparent from an early age. She finds love with Mary Llewellyn, whom she meets while serving as an ambulance driver in World War I, but their happiness together is marred by social isolation and rejection, which Hall depicts as typically suffered by "inverts", with predictably debilitating effects. The novel portrays "inversion" as a natural, God-given state and makes an explicit plea: "Give us also the right to our existence".
Jonathan Ned Katz is an American author of human sexuality who has focused on same-sex attraction and changes in the social organization of sexuality over time. His works focus on the idea, rooted in social constructionism, that the categories with which society describes and defines human sexuality are historically and culturally specific, along with the social organization of sexual activity, desire, relationships, and sexual identities.
Psychopathia Sexualis: eine Klinisch-Forensische Studie is an 1886 book by Richard Freiherr von Krafft-Ebing and one of the first texts about sexual pathology. The book details a wide range of paraphilias and focuses on male homosexuality/bisexuality. The book coined the terms "sadism and masochism" as well as borrowing the term bisexual from botanical language.
Androphilia and gynephilia are terms used in behavioral science to describe sexual orientation, as an alternative to a gender binary homosexual and heterosexual conceptualization. Androphilia describes sexual attraction to men or masculinity; gynephilia describes the sexual attraction to women or femininity. Ambiphilia describes the combination of both androphilia and gynephilia in a given individual, or bisexuality.
Feminist sexology is an offshoot of traditional studies of sexology that focuses on the intersectionality of sex and gender in relation to the sexual lives of women. Sexology has a basis in psychoanalysis, specifically Freudian theory, which played a big role in early sexology. This reactionary field of feminist sexology seeks to be inclusive of experiences of sexuality and break down the problematic ideas that have been expressed by sexology in the past. Feminist sexology shares many principles with the overarching field of sexology; in particular, it does not try to prescribe a certain path or "normality" for women's sexuality, but only observe and note the different and varied ways in which women express their sexuality. It is a young field, but one that is growing rapidly.
Bisexuality is a romantic or sexual attraction or behavior toward both males and females, to more than one gender, or to both people of the same gender and different genders. It may also be defined to include romantic or sexual attraction to people regardless of their sex or gender identity, which is also known as pansexuality.
Sexual fluidity is one or more changes in sexuality, sexual identity or sexual orientation identity. Sexual orientation is stable and unchanging for the vast majority of people, but some research indicates that some people may experience change in their sexual orientation, and this is slightly more likely for women than for men. There is no scientific evidence that sexual orientation can be changed through psychotherapy. Sexual identity can change throughout an individual's life, and may or may not align with biological sex, sexual behavior or actual sexual orientation.
Sigmund Freud was the founder of psychoanalysis. His views on homosexuality ascribed biological and psychological factors to explain the principal causes of homosexuality. Freud believed that humans are born with unfocused sexual libidinal drives, and therefore regarded homosexuality as a particular form of variation in the developmental process of the sexual function.
Sexuality and Its Discontents: Meanings, Myths, and Modern Sexualities is a 1985 book about the politics and philosophy of sex by the sociologist Jeffrey Weeks. The book received positive reviews, crediting Weeks with explaining the theories of sexologists and usefully discussing controversial sexual issues. However, Weeks was criticised for his treatment of feminism and sado-masochism.
Studies in the Psychology of Sex Vol. 2 is a book published in 1900 written by Havelock Ellis (1859–1939), an English physician, writer and social reformer. The book deals with the phenomenon of sexual inversion, an outdated term for homosexuality. It is part of Ellis' seven-volume series Studies in the psychology of sex. The book has seven chapters describing the prevalence, nature and theories in the 19th century about sexual inversion in men and women. Various case studies are presented and discussed. Ellis recognised a need to address the topic of sexual inversion especially in England:
... in England, more than in any other country, the law and public opinion combine to place a heavy penal burden and a severe social stigma on the manifestations of an instinct which to these persons who possess it frequently appears natural and normal.
Studies in the Psychology of Sex: Volume 7 is a book published in 1928 by the English physician and writer Havelock Ellis (1859–1939). Ellis was an expert of human sexuality but was impotent until the age of 60 and married to an open lesbian for much of his life. He later discovered that he could be aroused by the sight of a woman urinating. Terming this sexual deviation undinism, it is one of several topics covered in the seventh and final volume of his studies in the psychology of sex.
The history of bisexuality concerns the history of the bisexual sexual orientation. Ancient and medieval history of bisexuality, when the term did not exist as such, consists of anecdotes of sexual behaviour and relationships between people of the same and different sexes. A modern definition of bisexuality began to take shape in the mid-19th century within three interconnected domains of knowledge: biology, psychology and sexuality. In modern Western culture, the term bisexual was first defined in a binary approach as a person with romantic or sexual attraction to both men and women. The term bisexual is defined later in the 20th century as a person who is sexually and/or romantically attracted to both males and females, or as a person who is sexually and/or romantically attracted to people regardless of sex or gender identity, which is sometimes termed pansexuality.
LGBT portal 
