SharePoint Online is continuously evolving and improving, which is a great thing for you as a consumer of the service. One of the key features is the availability of modern sites, which are modern Office 365 group-connected team sites or communication sites, combined with improved functionality that can be consumed from a beautiful, responsive, modern user interface. All of this is great, but you might ask yourself, I have lots of classics (team) sites...how do I bring them into the modern SharePoint world? The answer is (in-place) modernization: you can fully transform (or "modernize") a classic site team sites into modern, optionally Office 365 group-connected, sites by following the SharePoint modernization guidance.