HUD is Heads Up Display in Ubuntu and is tightly integrated with the Unity interface. To stop it from running and eating CPU resources, you can do either of the following:
a. Install Xubuntu or Lubuntu
b. Not use Ubuntu at all, or;
c. Start up a terminal window by pressing Ctrl+Alt+T on your keyboard and type:
sudo chmod -x /usr/lib/indicator-appmenu/hud-service <enter>
This works well for laptops or desktops with less memory or CPU power and those that overheat (like mine :-).