A product key is a 25-character code that is used to activate a software product, in this case, Windows 7 Ultimate 32-bit. It is a unique identifier that is assigned to each copy of the software and is used to verify that the software is genuine and has not been pirated. The product key is usually found on a sticker or label on the packaging of the software or on a Certificate of Authenticity (COA) that comes with the software.