Many different things may cause turbulence, but each and every one of them is known and understood by pilots. Every day I fly, I expect a small amount of turbulence, just as I’d expect the odd bump in the road on the drive to work. Turbulence is uncomfortable but not dangerous. It is part of flying, and is not to be feared.
Different aspects of the weather cause different types of turbulence. CAT is an abbreviation for Clear Air Turbulence – the most common form of turbulence you are likely to experience.