A lot of people use the term “queer” in a lot of different ways.
The most common way I hear it used in my spaces is as a blanket term for all sorts of different non-straight and non-standard identities. It can encompass people who are gay and lesbian, bisexual, pansexual, questioning, etc., and many people also take it to include asexuals and/or trans people and/or people with non-standard gender identities (genderqueer, agender, two-spirited, and so on). In this way, it’s sort of like a shorthand for the increasingly long acronyms used to represent the non-straight/non-cis community (LGBTTIQQ2SA).
It’s a word with a tense history because it has traditionally been used as an anti-gay slur, but has been reappropriated by many folks as a more positive term, like how some lesbians refer to themselves as dykes. (With any term like this, it’s generally a good idea to wait until you hear someone call themselves that word before you call them it, if at all, just incase it’s something that bothers them.)