Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Office 2021 Professional is available to single customers.
Office 2021 Professional Plus is available to companies and organizations as a volume license (multiple copies). It includes all the applications of Office 2021 Professional, plus Teams.
Both are sold with a 'perpetual license': you pay once and you can use it thereafter without extra payments. This is different from Microsoft 365, which is a subscription product: you pay a monthly or yearly fee.