Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) are usually caused by the rapid switching action of semiconductors, relays, etc. resulting in electronic pollution. These affect the reception of broadcasts and can lead to the malfunctioning of other sensitive electrical and electronic equipment. Inverters etc. cause very severe interference over a wide frequency range, due to the very fast switching of components such as IGBTs.
Electromagnetic Interference refers to noise spread over the whole electromagnetic spectrum. Radio Frequency Interference refers to noise over the part of the spectrum used specifically for broadcasting.
EMI can be propagated in two ways: conducted interference along input and output cables, and radiated through direct transmission, capacitive and inductive coupling etc.