In Mac OS X you can hide an application with the key combination cmd⌘ + H. That the application is hidden you can not see directly in the Dock. Using this command, hidden applications are displayed with a translucent icon in the Dock:
defaults write com.apple.dock showhidden -bool true
To make the command take effect, you need to restart the Dock:
killall Dock
Revert to the default setting:
defaults write com.apple.dock showhidden -bool false
Screenshots:
Enabled (true)
Disabled (false)
