Some IT Definitions

End User Computing: (As defined by Wikipedia) (EUC) is a group of approaches to computing that aim at better integrating end users into the computing environment or that attempt to realize the potential for high-end computing to perform in a trustworthy manner in problem solving of the highest order.

Serial Numbers: (As defined at about.com) A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. A serial number for a piece of software is not usually the same as a product key but they are sometimes used interchangeably. You've probably seen serial numbers before. Nearly every piece of the computer has a serial number including your monitor, keyboard, mouse and sometimes even your entire computer system as a whole. Internal components such as hard drives, optical drives and motherboards also contain serial numbers.

Mac Address: (As defined by Geek.com) A Media Access Control address or MAC address is a unique code assigned to every piece of hardware that connects to the Internet. Internet capable phones, Network Interface Cards for desktop or notebook computers, Wireless Access Cards, and even some memory cards are among the devices that are assigned MAC addresses.
When a manufacturer creates a network capable piece of hardware they will assign the MAC address which will usually begin with a code that is tied to the manufacturer. The MAC address will be unique to every device, even two devices of the same type.

Unique Identifier: (As defined by Intertwingly.net) A unique identifier is a piece of data that unequivocally identifies something. On the Web, a URI is used as a unique identifier. A 128-bit GloballyUniqueIdentifier (GUID) is also common for software.