Electro Magnetic Interference
Whenever electrical current flows in a conductor (a standard wire or a wire on a printed circuit board, for example) it generates an electromagnetic field around this conductor. If this field is strong enough, it interferes in the circuits located near it – hence the name ”interference“.
The problem is that the inverse is also true: if we apply an electromagnetic field near a conductor we generate electric current on it. That’s why an electromagnetic field can interfere in an electrical circuit.
There are other forms of electromagnetic field. Generally speaking electromagnetic interference can be defined as ”electromagnetic disturbance, phenomena, signal or emission that causes or can cause a non-desired response, bad functioning or performance degradation in electrical and electronic equipments“.