What is the definition of risk category in a Risk Management plan?

As per the PMBOK guide the term Risk Category refers to "A Group of Potential Causes of Risk".

The whole purpose of Risk Categorization is to systematically identify risks in a consistent manner and organize them so that they can be better managed. It also helps to identify the root causes of these risks in a better way. A Risk Breakdown Structure or RBS is a classic example of this Risk Categorization idea. The RBS splits risks into categories and then splits them further into sub-categories thereby making our lives (The life of a Risk Manager) easier.