Adventure biking acronyms

Hey guys

I'm new to Adventure biking and at this present moment only know plastic bikes and their acronyms, seeing as I race in the offroad and enduro Championships.

So, seeing all these acronyms on adds just confuses me ... especially in the BMW sector.

Can you please clarify what the following stand for, any others one could come across? 

LC
GSA
The difference between a F and G model?

etc.

Thank you so much.