n.an elongated tethered balloon or blimp with cables or net suspended from it to deter enemy planes that are flying low
英汉双解大词典
barrage balloon
1.
N（名词）
one of a number of tethered balloons with cables or net suspended from them, used to deter low-flying air attack 防空气球; 一连串气球中的一个，气球上悬挂着缆绳或罗网，用来防止低空空袭