No, it’s not “the nine dots”. No, it’s not the “waffle”. It’s the App Launcher. Or more precisely – it’s the App Launcher icon – the App Launcher is the actual menu that appears when clicking on the icon.
If you’ve never seen this icon before, then you’ve most likely never logged into the Office 365 portal or used one of the online versions of Office.
Yes, you can call it anything you like. But if you want to best communicate about accessing the navigational menu Office 365, then it’s the App Launcher.