IMEI stands for International Mobile Equipment Identity. It refers to a code or number that identifies a specific mobile phone used over a mobile network. Every mobile phone has a unique IMEI number consisting of 15 to 17 digit number. Usually, it is printed at the back side of your mobile battery. You can check your mobile phone IMEI number by dialing *#06#.
IMEI number shows the information about the serial number of device, model number, and origin.
AA-BBBBBB-CCCCCC-D/EE
AA: It shows reporting body identifier. It is a part of TAC (Type Allocation Code) and shows mobile phone model and brand.
AA:BBBBBB: It is also a part of TAC (Type Allocation Code)
BBBBBB:CCCCCC: Shows serial number
CCCCCC:D: Luhn checksum
D:EE: Shows software version number
EE:IMEI number is used in the case of mobile theft. Telecom operators have a database with the IMEIs number. When a mobile is lost, that handset IMEI number is marked invalid and mobile operators will restrict the use of any SIM card. Although, a smart thief can install an unmark IMEI number on the stolen handset and can reuse it again which is illegal. So, if your phone is lost or stolen, you can provide your IMEI number to your mobile network provider and ask them to disable the phone.