The electromagnetic environment
Any electrical or electronic device creates what is called an electromagnetic (EM) environment as electrons are moved around to make the device work. In addition, there may be natural phenomena such as lightning occurring in the same location. Or for one of a variety of reasons, an electrostatic discharge may take place even when a device or system is not in its normal functioning mode.
Lightning over a city
When engineers first became aware of the effects of such phenomena, in the earliest days of radio, they usually referred to radio frequency interference (RFI). Today, the term electromagnetic interference (EMI) better reflects the fact that electrical and electronic systems may cause disturbances at any frequency between 0 Hz and the GHz (microwave) range.
For the purposes of its EMC-related publications, the IEC defines the EM environment as "the totality of EM phenomena existing at a given location."
Electromagnetic compatibility itself is defined as:
"the ability of an equipment or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment."