macOS: Name for app shortcut screen found by pinching with thumb and three fingers In macOS, what is the name for the app shortcut screen (with all the installed apps icons displayed, taking up the whole screen) found by pinching with thumb and three fingers together (or sliding-in 4 fingers together, alternatively) on Trackpad?
The screen is called Launchpad and is a feature built-into macOS. First introduced in Mac OS X Lion 10.7, it displays a grid of icons corresponding to installed apps. This feature was originally inspired from iOS which displays a similar grid of icons for installed apps.

This gesture is pre-defined for Trackpad, and can be turned on/off under System Preferences → Trackpad → More Gestures



There are other easy ways to invoke Launchpad too, which can be helpful on Macs without a Trackpad:


Keyboard: Press the special F4 key on your MacBook's built-in keyboard, or Apple keyboard. On newer hardware introduced after Mac OS X Lion was released, the key shows two rows of three squares to represent Launchpad.





Dock: Use the Launchpad icon in the Dock. The icon for the app is present by default in the Dock and looks like this:





Spotlight: Launchpad can also be invoked via Spotlight search:





Applications: Launchpad is available just like other built-in apps and can be found in /Applications directory in Finder. To invoke, double click on the app icon in Finder.




To learn more about Launchpad, go through the linked Apple Support articles:


Use Launchpad on your Mac
Use Launchpad to view and open apps on Mac