LGBT是女同性戀者(Lesbian)、男同性戀者(Gay)、雙性戀者(Bisexual)與跨性別者(Transgender)的英文首字母縮略字。1990年代,由於「同性戀社群」一詞無法完整體現相關群體,「LGBT」一词便應運而生、並逐漸普及[1]。在現代用語中,「LGBT」一詞、除了狹義的指同性戀、雙性戀或跨性別族群,也可廣泛代表所有非異性戀者[1][2]。另外,也有在詞語後方加上字母「Q」,代表酷兒(Queer)和/或對其性別認同感到疑惑的人(Questioning),即是「LGBTQ」。LGBT現今已獲得了許多英語系國家中多數LGBT族群和LGBT媒體的認同及採用,成為一種非常主流的用法[3][4]。坊間有不少LGBT的資源中心,提供不少有關LGBT的中文文章,包括醫學、心理學、社會科學及法律的文章,是一個研究LGBT議題人士搜尋資料的地方。
When sex is defined legally, it may be defined by any one of several criteria: the XY sex-determination system, the type of gonads, the type of external sexual features, or the person's social identification.[citation needed] Consequently, both transgender and intersex individuals may be legally categorized into confusing gray areas, and could be prohibited from marrying partners of the "opposite" sex or permitted to marry partners of the "same" sex due to legal distinctions.[citation needed] This could result in long-term marriages, as well as recent same-sex marriages, being overturned.[citation needed]

Dr. Alfred Kinsey's 1948 work Sexual Behavior in the Human Male found that "46% of the male population had engaged in both heterosexual and homosexual activities, or "reacted to" persons of both sexes, in the course of their adult lives".[13] The Kinsey Institute has stated that "Kinsey said in both the Male and Female volumes that it was impossible to determine the number of persons who are "homosexual" or "heterosexual". It was only possible to determine behavior at any given time".[13] Kinsey's book, and its companion Sexual Behavior in the Human Female, have received vocal criticism for their findings and methodology.[14][15][16][17] The New York Times called his research "conscientious and comprehensive"[18] and Professor Martin Duberman called it "skillful" and "a monumental endeavor".[19]
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