said, that (previously-mentioned person or object), aforementioned, you-know-(who, what, etc.)
A phrase used before a noun to refer to something or someone that both the speaker and the listener already know about from a previous conversation or shared experience. It acts like a definite article or the phrase 'the usual'.
The phrase
That person (we know) came again.
I bought that book (we were talking about).
Let's meet at the usual place.
How is that matter (in question) going?
This expression is highly dependent on shared knowledge between the speaker and the listener. It cannot be used if the listener has no prior knowledge of the topic being discussed. It often carries a nuance of 'the one we talked about before' or 'the one you know'.