License Glossary
What Is a Product Key?
A product key is the 25-character (5x5) code that verifies a software's authenticity. It is validated on Microsoft's server during activation and registers the license to the installation.
The key, in XXXXX-XXXXX-XXXXX-XXXXX-XXXXX format, can come from the Retail, OEM or volume channel — the channel defines the key's terms of use.
O/0 and I/1 mix-ups are the most common entry errors; typing manually instead of pasting resolves some failures. Store your key safely together with your purchase email.
What you should know
- 25 characters, written in blocks of five
- The key's channel (Retail/OEM/Volume) defines its terms — visible via slmgr /dlv
- O/0 and I/1 confusion is the most common entry error