Definition: Product activation is the procedure by which a piece of software or operating system is proven to be legitimately installed.
From a technical perspective, product activation usually means combining a product key or serial number with unique information about a computer and sending that data to the software maker over the Internet. This helps prove that the product key or serial number being used is not pirated and that the software is being used on an appropriate number of computers... usually, but not always, one.
Depending on the software or operating system, choosing not to activate might prevent the software from running, reduce the functionality of the software, cause regular (annoying) reminders, or may not have any effect at all.
Also Known As: activation
Examples: "After Windows 7 was done installing, I activated it so I could be sure to receive all the updates necessary for my computer."