私下活动

secret activities

私下告诉

tell in secret

这是背着人私下办的。

This was done in secret without telling anyone.

这是人家私下告诉他的。

Someone told him this in secret.

私下决定

make a decision in private

私下调解

mediate in confidence

私下会晤

meet in private

私下协商

negotiate in private