I see the following definition in the glossary:
Dropdown: The panel is displayed when you click on a badge. That panel contains alerts or notices depending on which badge you have clicked.
Various words have been used by different people for this element: flyout, flyout menu, dropdown, dropdown menu, notification panel. This seems like our chance to, ideally, standardize our term and, minimally, to at least acknowledge that it's called a variety of things. (My own bias: this is not a "menu.")
Here's a list of terms I'd deem acceptable. Vote for your favorite.
Notification dropdown JM