What's the difference between Office 365 and Office 2016 or 2019?

Subscription v Product

The difference between Office 365 and a year-branded version of Office, like Office 2016 or Office 2019, is how it is purchased.

Office 365 is a subscription, where the features and services are always up-to-date and improving. Rights to use Office 365 continue so long as the subscription is paid and maintained.

A year-branded version of Office is a static product. Its features remain the same and it will only receive updates to fix security issues and problems with the software. It does not receive feature updates. It is purchased once, providing a licence that continues forever.

Further Explained

Office 365 is Microsoft's primary productivity product. It is a monthly subscription available to businesses and individuals, with a number of subscription tiers.

Typical Office 365 subscriptions for businesses include traditional Microsoft Office apps, like Word, Outlook and PowerPoint. They also include online services like Teams, Planner and more. Features of both apps and services are increasingly integrated and available online.

Microsoft updates apps at semi-regular intervals, typically 6-12 months. Services are continually, but irregularly, improved and changed.