An icon that is commonly used on graphical interfaces to mean "wait until finished." When the hourglass icon appears, you cannot do anything within that part of the application until that task has completed and the hourglass goes away.

An hourglass is a centuries-old device for counting time. It consists of two glass chambers attached to each other via a tiny opening. Half filled with sand, when the hourglass is turned over, the sand falls from one chamber to the other. The amount of sand and size of chambers and opening are precisely measured so that when all the sand from one side falls to the other, a certain amount of time has passed. See hourglassing.