The "busy" pointer in earlier versions of Windows. Newer versions have a spinning circle. Both of these pointers mean "wait until finished." When they appear, nothing can be done in the application until the hourglass or circle goes away. In many cases, the program has to be ended by force or the computer must be rebooted.
What's an Hourglass?
An hourglass is a centuries-old device for counting time. It comprises two glass chambers connected via a tiny opening. Half filled with sand, when the hourglass is turned over, the sand falls from top to bottom. The quantity of sand and size of opening are precisely measured so that when all the sand has fallen to the bottom, a certain amount of time has passed. See
hourglassing and
Mac pinwheel.