Risk Aversion/ Risk Appetite

Hey guys
Being new to forex trading and as i am learning and also doing live trading i have few questions. Can someone clear the concept of risk appetite and risk aversion and risk on and risk off? Also how are equity markets related to the risk and what exactly is involved in equities? I hear these words almost everyday. I know somewhat but i wanna grasp the whole concept. If someone can guide me , i will really appreciate it.
Regards
Gary