The Unity desktop HUD or heads-up-display was introduced for the release of Ubuntu 12.04 and it has received much attention. The HUD is meant to be an alternative to the menus provided for individual applications.
About The HUD
The HUD can be used to find all of the actions and options which are available for the highlighted applications. You can also use the HUD to search through actions inside your application indicator menus.
Unity Desktop HUD Tips
Here are some helpful details and tips to help users get the most out of the Unity desktop heads-up-display or HUD.
Display The HUD
You can display the Unity desktop HUD at any time with the Alt keyboard key. This is not to be confused with the Unity dash which uses the meta or Windows keyboard shortcut. After it opens you can begin typing in a command or action for the currently highlighted application.