The gourd is a member of the plant family Cucurbitaceae and a relative of the pumpkin. When dried, its fruit can be hollowed out and used as a container. It is also used as food.
Most commonly depicted on Danbooru is the dumbbell-shaped fruit of the bottle gourd, or calabash, which can be used to hold liquids like sake.
The following tags implicate this tag: holding_gourd (learn more).