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, natural phenomena such as lightning may occur in the same location. Also, for 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 these effects, in the early days of radio, they usually referred to them as 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 equipment or a system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment".