EMI: electromagnetic waves interact with electronic components and cause Interference, which is called EMI.
There are two kinds of interference: conduction interference and radiation interference.  Conducted interference refers to the coupling (interference) of signals on one electrical network to another electrical network through a conductive medium.  Radiated interference refers to an interference source coupling its signal (interference) across space to another electrical network.

EMC (Electro Magnetic Compatibility) refers to the ability of a device or system to operate in accordance with its electromagnetic environment without causing intolerable electromagnetic interference to any device in its environment.
Therefore, EMC has two requirements:

On the one hand, the electromagnetic interference generated by the equipment in the normal operation of the environment cannot exceed a certain limit;

On the other hand, it means that the appliance has a certain degree of immunity to electromagnetic interference existing in the environment.