essential performance
Beginner
The jobs a medical device must keep doing right so that patients are not hurt.
Novice
In the medical-equipment safety standard IEC 60601-1, the functions whose loss or degradation would put a patient at unacceptable risk. Tests are judged against them.
Expert
Identified through risk management and used to set test pass criteria, for example that electromagnetic interference must not cause unintended or unsafe stimulation.
Explained in Medical devices (Industries).