noun
A long, narrow excavation. 濠 is a rare variant used when the trench is filled with water (moat).
城の周りには深い壕が掘られていた。
A deep moat had been dug around the castle.
敵の侵入を防ぐために壕を掘った。
They dug a trench to prevent the enemy from invading.
noun
air-raid shelter; dugout
Only when written 壕
Specifically an underground shelter used during air raids. Written only with 壕.
戦時中、人々は壕に避難した。
During the war, people took shelter in air-raid shelters.
The kanji 壕 and 濠 are both composed of 土 (earth) and phonetic components, originally referring to ditches or moats. The distinction between dry (壕) and water-filled (濠) is a later convention.