or more exactly

Our friends, that is to say our son's friends, will meet us at the airport. 我们的朋友，更确切地讲是我们儿子的朋友，将在机场接我们。

said when you want to give further details or be more exact about something

I'll meet you in the city, that is, I will if the trains are running. 我们城里见，那就是说，只要火车还开我就会见到你。