A 15 digit, unique serial number assigned to a mobile&nbsp;
phone. IMEI consists of five groups of numbers. The&nbsp;
first group represents the manufacturer; the second&nbsp;
sequence identifies the Type Approval Code (TAC) or&nbsp;
model number; the third represents Final Assembly&nbsp;
Code (FAC); the fourth is the device serial number&nbsp;
and the fifth is a spare single digit (usually 0).

A 15 digit, unique serial number assigned to a mobile  phone. IMEI consists of five groups of numbers. The  first group represents the manufacturer; the second  sequence identifies the Type Approval Code (TAC) or  model number; the third represents Final Assembly  Code (FAC); the fourth is the device serial number  and the fifth is a spare single digit (usually 0).

Glossary

International Mobile Equipment Identity