Wim: BS is that what you try to avoid while walking in a cow pasture. Actually, this is really CS. BS is considerably deeper and much harder to get off your feet.
BS is a term used in this country usually to describe something that is totally wrong and is not worthy of consideration.
CS, not to be confused with cows, is usually things that are small and irrelevant.....but not very nice.....as in walking around in a yard full of chickens.
No doubt that you have similar slang descriptions in your language there really is no need to learn them. It's all BS.