This is an hourglass made up of two glass balls and a narrow connecting tube. When all the sand in the hourglass flows into the light bulb at the bottom, it means that time has passed. It should be noted that the sand displayed by the Apple system is earthy brown, while most of the other systems display golden sand. Therefore, the expression can be used not only to specifically refer to the hourglass, but also to express meaning related to time and hourglass graphics.
