A bag filled with sand; used as a weapon or to build walls or as ballast WordNet 3.0 & Open English WordNet

A sandbag or dirtbag is a bag or sack made of hessian, polypropylene or other sturdy materials that is filled with sand or soil and used for such purposes as flood control, military fortification in trenches and bunkers, shielding glass windows in war zones, ballast, counterweight, and in other applications requiring mobile fortification, such as adding improvised additional protection to armored vehicles or tanks. Wikipedia

Obstruction device commonly used in flood control and temporary military fortifications. Wikipedia Disambiguation

Device commonly used in flood control and temporary military fortifications Wikidata

A sturdy sack filled with sand, generally used in large numbers to make defensive walls against flooding, bullets, or shrapnel. Wiktionary