Queer is an umbrella term for people who are not heterosexual or cisgender. Originally meaning 'strange' or 'peculiar', queer came to be used pejoratively against those with same-sex desires or relationships in the late 19th century. Beginning in the late 1980s, queer activists, such as the members of Queer Nation, began to reclaim the word as a deliberately provocative and politically radical alternative to the more assimilationist branches of the LGBT community.

In the 21st century, queer became increasingly used to describe a broad spectrum of non-normative sexual or gender identities and politics. Academic disciplines such as queer theory and queer studies share a general opposition to binarism, normativity, and a perceived lack of intersectionality, some of them only tangentially connected to the LGBT movement. Queer arts, queer cultural groups, and queer political groups are examples of modern expressions of queer identities.

Critics of the use of the term include members of the LGBT community who associate the term more with its colloquial, derogatory usage, those who wish to dissociate themselves from queer radicalism, and those who see it as amorphous and trendy. Queer is sometimes expanded to include any non-normative sexuality, including cisgender queer heterosexuality, although some LGBTQ people view this use of the term as appropriation.