Definition
Indicates that there was a period in the past when something was true or used to happen.
往昔；以前
Time was when this street was full of small shops.
曾經有段時間這條街上都是小商店。
Time was when people used to write letters to stay in touch.
曾經有段時間人們會寫信來保持聯繫。
Time was when we would often picnic by the lake in the summer.
曾經有段時間我們夏天經常在湖邊野餐。