is a subscription-based service. That is, instead of buying a copy of the suite directly for a one-time upfront cost, users instead pay a monthly subscription fee to access the service at a level of their choice. MS Office 365 Product Key 2021, users always have access to the latest version because the platform will end up being updated by Microsoft, while on-premises users would have to buy a new copy of the latest version on-site to use it .