in between
in between意为：在……之间。其作用仍相当于介词。如：
There are trees in between the buildings. 大楼之间有树。
It’s somewhere in between New York and Chicago. 它位于在纽约和芝加哥之间的某个地方。
有时可用作副词。如：
He has breakfast and supper and doesn’t eat anything in between. 他只吃早餐和晚餐，其间什么也不吃。
以上各用法中的介词 in 有时也可省略，而只用 between.