OSX 10.8 Mountain Lion does not give you the option to quit the Finder by default. This can be annoying if you want to hide your desktop icons and concentrate on current the task in hand.
You can add the Quit option to Finder menu with the following terminal commands:
defaults write com.apple.finder QuitMenuItem 1 killall Finder
If you want to remove it again use the following:
defaults write com.apple.finder QuitMenuItem 0 killall Finder