Why my application icons wiggle when I press ALT key in Launchpad? I tried Launchpad first time today and went through the common modifier keys &amp; their combinations to see if some hidden options appear.

When I pressed ⌥ ALT all the apps started wiggling. What does it mean?
Wiggle is the edit mode. (so you can delete or uninstall the apps that came from the app store) 

Holding alt is the quickest way to enter edit mode.