What is the thing called in GNOME 3 that appears when you press the super key?

When using Ubuntu 16.04 with the GNOME desktop and pressing the super key it causes an overlay to appear that displays Workspaces, overview of Applications, Application Launcher on the left, and search at the top.

I'm wondering what this feature is called?

It's generally called the "(Activities) Overview":

Activities Overview

This is a separate view designed to enable users to get an overview of their current activities and to enable effective focus switching (in this regard, the overview is a facilitator and a mediator, not a destination). The top bar continues to be displayed in the overview in order to provide a familiar landmark and visual anchor.

It's composed of:

• the dash,

• the window picker,

  

• the application picker,

  

• the search,

• the workspace switcher, etc.

We also have a tag for it: activities-overview