tracer
noun [ C ] uk/ˈtreɪ.sər/ us/ˈtreɪ.sɚ/
曳光弹
a bullet that leaves a line of flame or smoke behind it when it is fired, so that you can see the direction it has taken
Tracer bullets streaked through the sky. 曳光弹划过长空。
The sky was bright with tracer fire. 曳光弹发出的火光照亮了天空。