Risk describes a factor that may have a negative OR a positive impact on a project. A positive risk is also called an opportunity in general. Risk is quantified by measuring the probability of an unexpected event occurring with an impact that event would have on your project.
Risk audit is the examination and documentation of the effectiveness of risk responses in dealing with identified risk and their root causes, as well as the effectiveness of the risk management process.
The risk management plan referred to in the PMBoK is the beginning of managing risk. The work that is done within a manufacturing process for example is also governed by Operational Risk Management. This is a process that begins in the planning phase of a project and continues throughout project execution and ends with the project close out.