q.t.

All the arrangements were made on the q.t.所有安排都是秘密进行的。

She told me about it on the q.t.她悄悄告诉了我这事。

This information is private, so keep it on the q.t. [=don't tell anyone about it]这个消息涉及隐私，所以不要告诉别人。