Hourglass is an object, usually made of glass, which is used to measure a period of time through the flow of fine sand.

Unlike the sundial or the gnomon it does not depend on the sun to measure time. Also, it allows like the water-clock to measure a period of time, night and day.

The hourglass is an object that has been regularly used, and is sometimes still used, to measure time for games for example or historically sometimes for speeches.