QUILTBAG is like LGBT, or LGBTQ, or LGBTQ, or LGBTQIAA, etc. It's just an acronym to describe the community of people. I use it mostly because it's funny, but also because it's more inclusive then LGBTQ+. Really, if i'm being serious the one I like the best is GSM, which stands for Gender and Sexual minorities.
I think QUILTBAG is generally accepted as being Queer, Undecided, Intersex, Lesbian, Trans, Bisexual, Asexual, and Gay, but honestly the letters all get reassigned all the time because sometimes the GSM community just likes making its own life more complicated.
As for lingo, man, there's so much. Some of it is serious, and some of it is the community having a laugh at itself while describing common life experience
Passing is a very common one. It basically means presenting as the gender you wish to be seen as and raising no eyebrows, or not being what one could describe as "visibly" outside of the gender binary.
If you can do this - because not everyone can, or wants to - it is said that you have "passing privilege". Some people desire this because it is safe, or safer to be a trans person if you can pass as cisgender.
Cisgender just means that your gender and the gender the doctor assigned you at birth are the same. I'd say that your Gender and Sex are the same, but the truth is that unless you've actually had it tested, you probably don't know what your chromosomes actually are, and they might be different from what you think they are.
A "Beard" is a term that describes an opposite-sex partner for a same-sex attracted person, usually for the purpose of deceiving unaccepting relatives, but occasionally sometimes when they're lying to themselves, too. In some cases the Beard is complicit (it's usually much better this way), but in other cases the Beard is being strung along and it's a gross situation.
I can add more if people want, and other people who are hanging out and are part of the GSM community can add some too.