Definition
Referring to a time in the past, often when reminiscing about positive aspects of that period.
昔日，往昔（常用于追憶美好的往事）
Back in the day, this town was full of lush orchards.
在过去，这个城镇到处都是茂盛的果园。
Back in the day, our school days were so carefree.
在过去，我们的学校生活是那么无忧无虑。
I remember back in the day, everyone would dance at the block parties.
我记得在过去，每个人都会在街区派对上跳舞。