defining moment
noun [ C ] uk/dɪˌfaɪ.nɪŋ ˈməʊ.mənt/ us/dɪˌfaɪ.nɪŋ ˈmoʊ.mənt/
转折点;决定性时刻;关键性事件
the point at which a situation is clearly seen to start to change
The end of the Cold War was a defining moment for the world in more ways than one. 从很多方面来讲，冷战的结束是世界的一个转折点。