through a wall; on the other side of a wall
Describes hearing, sensing, or communicating through a wall. Often used adverbially as 壁越しに.
壁越しに隣の部屋の話し声が聞こえた。
I could hear voices from the next room through the wall.
壁
I talked to him through the wall.
Compound of 壁 (wall) and 越し (across, through).