For the past decade or so, Microsoft has released updated software every three years.
Office 2019 is a one-time purchase of the basic Office Suite (Word, PowerPoint, Excel, OneNote, and Outlook). These static versions can be downloaded to one (1) computer. You have access to security updates only. To upgrade to new features, you must wait for, and purchase, the next release of Office.
Office 365 is a subscription-based service that provides the basic Office Suite as well as access to multiple services (OneDrive, Flow, Teams, etc.). These services vary with licensing. A common example is Office Pro Plus (one of the options included with Office 365 licensing), which allows you to download apps to multiple devices, and to receive regular feature, security, and service updates as soon as they are available.
How this relates to QuickHelp Content
If you have the one-time purchase of Office 2019, and are looking for content related to Word, Excel, Outlook, and PowerPoint, please refer to the 2016 content for each respective app. We have added new feature updates through the release of 2019, so these assets are the most relevant to your needs.
If you have the Office 365 subscription-based service and are looking for content related to Word, Excel, Outlook, and PowerPoint, please refer to the {{APPLICATIONNAME}} for Office 365 content. QuickHelp keeps content updated and relevant as new features are added.