Definition: The adjective used to describe people whose enduring physical, romantic and/or emotional attractions are to people of the same sex. Avoid identifying gay people as "homosexuals" as it can be offensive to many lesbian and gay people.
In other words, it's a word to usually describe males who are attracted to the same gender. Lesbian is usually a preferred term for woman though there are some lesbians who actually prefer being called gay than lesbian
PLEASE for the love of god, AVOID calling something/someone gay when they aren't. For example, calling your friend "gay" when they aren't actually gay is offensive to most gay people. Calling inanimate objects gay is also offensive.
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The LGBTQ+ Guide (includes romantic orientations+)
RandomThis is a book that will help you understand the different meanings to the aromantic and sexual orientation spectrums