Electromagnetic compatibility (EMC) is the branch of science and engineering concerned with the design and operation of equipment in a manner which makes them immune to certain amounts of electromagnetic interference, while at the same time keeping equipment-generated interference within specified limits. The scope of EMC is thus very wide as it encompasses virtually all equipment powered by electrical supplies. Practically, all engineering systems incorporate power conditioning and information processing units and thus fall within the scope of EMC. The frequency range of interest extends from DC to light and in certain parts of this spectrum a strict international regulatory framework has been set up to ensure immunity of equipment to electromagnetic interference (EMI) and to control emission.
From "Principles and Techniques of Electromagnetic Compatibility", Christos Christopoulos, 1995 CRC Press, ISBN 0-8493-7892-3.