Queer is an umbrella term used to describe sexual and gender identities other than straight and cisgender. It is a word that has evolved over time and has been used in different ways and meanings. Originally, it meant "strange" or "peculiar" and was used pejoratively against those with same-sex desires or relationships in the late 19th century. By the 20th century, it was used as a pejorative term to refer to men who were perceived as flamboyant. However, in recent years, the term has been reclaimed by the LGBTQ+ community and is used with pride to identify themselves.
Queer is sometimes used as an umbrella term to refer to all people with non-heterosexual sexual orientations or all people who are marginalized on the basis of sexual orientation. It can also be used to express that sexuality and gender can be complicated, change over time, and might not fit neatly into either/or identities, like male or female, gay or straight. Queer can be a label claimed by a person who is attracted to people of many genders or who feels that they personally don’t fit into dominant norms, due to their own gender identity/expression, their sexual practices, their relationship style, etc. . Many people claim the label queer as a badge of honor that has a radical, political edge.
It is important to note that the word "queer" has a history of being used as a derogatory term thrown at LGBTQ+ people, and some still see it as a degrading slur. Therefore, it is best to ask what labels people prefer and not call someone "queer" unless you know theyre cool with it.