IMEI stands for International Mobile Electronic Identifier. It is a unique number exclusive to your device. The IMEI is your phone's official ESN (Electronic Serial Number). 

IMEI numbers are typically 12-14 digits in length. The most important thing to know about an IMEI number is that it is a unique ESN that no other phone has and is required to activate your phone.

A phone's MEID/IMEI number can be located in several ways:

1. It is typically located on a sticker behind your phone's battery (provided your phone has a removable battery).

2. It is typically printed on the box your phone arrives in.

3. It can also be easily located within your phone's Settings console under about/general.