UDID or UUID of iPhone devices

UDID or UUID of iPhone devices

• When manufactured every iPhone is assigned an identifier that is unique to that physical device.
• This is known as the UDID ("Unique Device Identifier "), but is also commonly referred to as the "UUID", an acronym for Universally Unique Identifier
• UDID is a 40 digit Hexadecimal number
• UDID is a must for provisioning of the device

How to Find UDID:- 

• Connect the Device to iTunes 
• Click on Device name present on left side of Panel 
• Click on Summary (It shows device summary) 
• Click on Serial number  
• It shows you the 40 digit hexadecimal number

Use of UDID: It is basically used for Device Provisioning.

For QA you have to just copy and paste it using Edit button of iTunes and provide this number to developer so that they can add it to provisioning file which came along with testing builds.