At some point in the past week or so, you might have found that your PC has installed a new version of Office on your PC. Moreover, it's been installed alongside the version of Office that you already have. This second version of Office is the suite of web apps, and they're showing up on PCs without users' permission.
There's no need to get upset about some conspiracy about Microsoft forcing you to put a new version of Office on your PC, especially when you're already running the productivity suite. As it turns out, this is a bug in the Edge browser and it's being fixed.
Here's the deal. Microsoft has historically added pinned Office web apps in the Start Menu, but they were simply links to the apps, which would open in a tab in the browser. However, these would only show up if Office wasn't already installed. Due to a bug, these pinned websites were converted to being installed as apps, even if you have Office installed. Being installed as an app means that it opens in an Edge window that looks like a separate app, without tabs or an address bar.
As it stands right now, the rollout of this change is being paused while Microsoft fixes the issue. If you've been affected by the issue, you can get rid of the Office web apps through the Control Panel or Settings.