For much of the 20th century, "queer" was an insult. Activists began reclaiming it during the AIDS crisis, when groups such as Queer Nation, founded in New York in 1990, used it to signal a confrontational politics. In 1990, scholar Teresa de Lauretis introduced the phrase "queer theory," which became an academic field studying how sexuality and gender are constructed.
Today many people use queer because it is broad and does not require choosing a narrower label. It is the Q in LGBTQ for many organizations. Some older LGBTQ people still hear it as a slur, so it is best used for people who claim it.
Queer also carries a political meaning: a challenge to systems that define some families and bodies as normal. Black queer thinkers such as Audre Lorde, James Baldwin and Cathy Cohen connected queer life to struggles against racism and poverty.