The term “UDID” is occasionally thrown around when discussing privacy or development topics concerning the iPhone. I’m sure that we all don’t know what “UDID” stands for, so I thought I would explain the purpose of a UDID.

A UDID, or “Unique Device Identifier,” is simply a specific serial number for your iDevice. There are multiple advantages to having this device-specific serial, but it mainly serves as a way to document the existence of your device and to track it.

Think of your iPhone’s UDID as its social security number. It is a 40-number, alphanumeric string that is not replicated on any other iDevice…

Your UDID is also important because it is the way that most ad companies profile cellphone users for marketing purposes. Lately, there have been a lots of issues raised about iOS apps sending UDID numbers to ad companies without the user’s permission.

If you are familiar with the world of app development, you are already very familiar with the UDID. Apple allows developers a way to beta test iOS apps with up to 100 iDevices. You have to supply the developer with your UDID in order to install these beta, ad-hoc applications.

To find your iPhone’s UDID, plug your iPhone into iTunes. Click on your iPhone in the list of devices and look at its summary. You will see Name, Capacity, Software Version, Serial Number and Phone Number. Click on the Serial Number and it will change to show you your UDID.

Even if you’re not in the world of app development, it’s always good to be informed. If you’re interested, you can read an article by the Wall Street Journal on how app makers are using your device’s UDID.

Did you know your iPhone had a UDID?