These are vertical standards that apply to specific types of equipment. A Particular Standard takes precedence over the General Standard. Examples include:
This is defined as the performance of a clinical function, other than that related to safety, where loss or degradation below the manufacturer's specification results in an unacceptable risk. iec 60606 pdf
Example: An MRI machine produces images. If the image distorts, it may not be a safety issue. However, if the patient table moves unexpectedly during a scan due to a software glitch, that is a failure of Essential Performance because it creates a direct physical hazard. The Ultimate Guide to IEC 60606 PDF: Understanding
This is the base document. It applies to all medical electrical equipment. It covers general requirements for electrical safety, mechanical safety, protection against fire, and labeling. The current active version is generally the 3rd Edition, with the 2nd Edition being phased out globally. IEC 60601-2-11: Gamma beam therapy equipment