EMC (Electromagnetic Compatibility) and EMI (Electromagnetic Interference) are closely related concepts in the field of EMC testing of electrical & electronic products for EMC compliance, but the EMC and EMI are not the same thing. 

What is EMI?

An electrical and electronic product usually emits some amount of unwanted electromagnetic energy during its operation. The unwanted electromagnetic energy emitted from the product is called EMI (electromagnetic interference), which can affect the performance of or sometimes damage the electronic device(s) operating in the same environment.

The sources of EMI can be any electrical & electronic device and sometimes EMI can occur naturally due to environmental events, such as electrical storms and solar radiation.

What is EMC?

Electromagnetic Compatibility (EMC) is the capability/ability of an electrical & electronic product to withstand EMI from nearby devices & operate properly as intended, at the same time, not emitting more than a specified level of EMI. 

To reduce the risk of the EMI, the products are designed to meet the requirements of EMC standards. When a product meets the requirements of the EMC standards, the product is said to be EMC compatible/EMC certified product (i.e., withstand EMI from nearby devices & operate properly, and not emit more than a specified level of EMI) and can sell in the market.