Wiktionary
n. The study, based on critical theory, of issues relating to sexual orientation and gender identity, usually focusing on LGBT.
Wikipedia
Queer studies, sexual diversity studies, or LGBT studies is the study of issues relating to sexual orientation and gender identity usually focusing on lesbian, gay, bisexual, transgender, queer, questioning, and intersex people and cultures.
Originally centered on LGBT history and literary theory, the field has expanded to include the academic study of issues raised in biology, sociology, anthropology, the history of science, philosophy, psychology, sexology, political science, ethics, and other fields by an examination of the identity, lives, history, and perception of queer people. Marianne LaFrance, the former chair of the Larry Kramer Initiative for Lesbian and Gay Studies at Yale University, says, "Now we're asking not just 'What causes homosexuality?' [but also] 'What causes heterosexuality?' and 'Why is sexuality so central in some people's perspective?'"
Queer studies is not the same as queer theory, an analytical viewpoint within queer studies (centered on literary studies and philosophy) that challenges the putatively "socially constructed" categories of sexual identity.