step change
noun [ C ] mainly UK uk/ˈstep ˌtʃeɪndʒ/ us/ˈstep ˌtʃeɪndʒ/
阶跃变化，步进变化（在某一局势下，比常规大得多的变化）
a change in a situation that is much bigger than usual
There is a step change taking place in communications technology. 通讯技术取得了较大的变化。