Hey Radicals!!

I guess I'm part of the old guard and wanted to ask a question that maybe obvious to some, but isn't to me.

What is queer?

As a kid growing up, I had the feeling that it meant "gay/homosexual," but after perusing /r/sexpositive, and linking over to you, i get the feeling that either the term has expanded, or I didn't understand it fully. Does it mean anything "not straight?" Does it have a masculine and/or feminine connotation? Is it a slang term for the whole LGBT community? Is it an umbrella term that has different nuances for different people?

Just wanted to know how to flow with this group and don't want to offend!!

Thanks for the clarification & helping those of us who are trying to navigate these modern waters!

EDIT - as a side question...Does the "Radical" part just mean you're all awesome? Or just come with a sweet, rowdy, fuck-you attitude? ;)