IMEI stand for The International Mobile Equipment Identity, it is a number unique to every GSM, WCDMA, and idem mobile phone, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone.
1 Additional Answer
International Mobile Equipment Identity (IMEI) is the distinctive electronic serial number that is given to mobile phones when they are being manufactured. If the phone is stolen or lost the police or insurance company can use it to block the phone.