IMEI number or International Mobile Equipment Identity is a unique serial or identification or the serial number of a mobile and smartphones. It is a 15 digits unique number of a mobile. You can see it on your phone, below your battery or in your phone' s packing box also.
This number can help you to prevent your phone being used by someone else if the phone is lost and got by someone else, or stolen. But sometimes, we need to change android IMEI number of our mobile.