A bag filled with sand or earth, used for flood control, fortifications, or as a weight.
We stacked sandbags in preparation for the flood.
土のうは水害対策に欠かせない。
Sandbags are essential for flood control measures.
Compound of 土 (do, 'earth') and 嚢 (nō, 'bag'). The kana-mixed spelling 土のう is now standard.