Product key
Alternatively called an activation code, CD key, license key, product id, registration key, and serial key, a product key is a group of numbers and letters for preventing software piracy. Software that requires a product key cannot be installed on a computer until a valid number is entered.
A product key should not be called a serial number to help prevent confusion with a computer or hardware products serial number.
Above is an example of the Microsoft Windows XP Home Edition product key. Usually, it is on the side or bottom of an OEM (original equipment manufacturer) desktop computer. On an OEM laptop, it may be on the bottom of the laptop, or underneath the laptop battery. In this example, the last four sets of letters and numbers are hidden to protect the unique key. After Windows is installed on a computer, it prompts you for an activation key to verify your computer has a legitimate copy of Windows. Below, are the formats of the Microsoft Windows product keys.
Windows 10, 8, 7, Server 2008, Vista, Server 2003, XP, 2000, Me, and 98
Product Key: xxxxx-xxxxx-xxxxx-xxxxx-xxxxx
Windows 95 and NT
Product Key: xxxxx-xxx-xxxxxxx-xxxxx
Where do I find the CD key, product key, or unique number?
Microsoft Windows product key
For computers, if you have an OEM PC (e.g., Dell or Hewlett-Packard), the Windows product key is found on the side or bottom of the computer.
Windows 10 upgrade users
If you have installed the free Windows 10 upgrade, the unique key is associated with your Microsoft account and can be re-activated after reinstalling Windows 10.
Software product keys
If you are looking for your program CD key, it's found on the CD sleeve, jewel box, or the printed documentation included with the disc.