Political Correctness

Can someone please explain to me the term “Political Correctness”. I really don’t understand….for example, I always assumed the term “guy” came from Guy Fawkes….he was...to the best of my knowledge, a man. “Gals” on the other hand I assumed was a slang variation of girls. Now if I’m even close….why do we now refer to everybody as guys when clearly a lot are female and therefore “gals”. Further to this, it has always been accepted that females have had ess on the end...lioness, actress etc. mind you it appears to be selective because there are still duchesses we don’t refer to them as duches do we? What about baa baa coloured sheep? How ridiculous...if they are black...call them black I am quite sure they wont be offended. Why do forms to be filled now ask...male/female/other? If I drop my pants I can tell immediately that I'm male if my wife drops hers I can tell I'm in for fun....oops sorry, I can tell immediately that she is female....so just who are the "others"?