A Microsoft product key is a unique 25-character code used to activate Windows or Office. It typically looks like this: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

Subscription-based services often do not require a key once you have linked your purchase to your Microsoft account. You simply sign in to activate.

Organizations often use "Generic Volume License Keys" (GVLKs) for mass deployment, such as the keys provided for Office LTSC Standard 2021 . Staying Safe Online

In recent years, Microsoft has shifted toward digital licenses and subscriptions: