Hourglasses, also known as sand clocks, are time-measuring devices that have been used since ancient times. They consist of two glass bulbs connected by a narrow neck and filled with sand or other granular material. As the sand passes through the neck, it measures out a certain amount of time. The term 'hourglass' is derived from the fact that these devices were traditionally used to measure out an hour's worth of time. The crossword solution for this term is 'timers, ' which refers to any device that is used to measure and keep track of time.