Quick Look is when you select a file in the Finder and press the spacebar to view its contents in a window. You can also view the contents full screen by holding the option key when pressing the spacebar. This is a shortcut for the full screen button that appears at the bottom when you just press the spacebar. You can’t use this option key shortcut in other Quick Look situations, like open/save dialogs, but you usually still do get the full screen button at the bottom.
Mac Video Tutorials and Tips for Apple Users
