somehow strange, odd, or unusual, deviating from what is normal or usual, often used to refer to a person whose nature/behavior is unconventional or eccentric;
e.g. I thought it was queer that she did not want to come with us. He was a queer old man with strange habits.
(adjective)
having a sexual orientation that is not heterosexual and/or a gender identity that is not cisgender, in other words, not solely attracted to people of the opposite sex and/or not identifying as strictly male or female (may be used as a derogatory/offensive term);
e.g. He realized that he was queer when he was in college.
(noun)
a person who does not identify as heterosexual and/or cisgender (may be used as a derogatory/offensive term);
e.g. She was glad to meet someone who was a queer like her.