fast意思是"快"，fast lane的意思是公路上的快车道，life in the fast lane是指竞争激烈、忙碌而快节奏的生活方式。

【例句】
Bill used to enjoy life in the fast lane in New York, but his family didn't.
比尔原来喜欢纽约那种紧张的大都市生活，他家人却受不了了。

When Curtis turned forty, he decided he needed to live life in the fast lane, so he quit his job as a dentist and decided to tour Europe by motorcycle.
当柯蒂斯四十岁的时候，他决定要在过有挑战性的生活，于是他辞去了牙医的工作，决定骑摩托车去欧洲旅行。