that is (to say)
idiomPart ofthat
that is (to say) — idiom
1. used to explain what you mean more clearly or to correct or add detail to what y
1.idiom
Definition
used to explain what you mean more clearly or to correct or add detail to what you have just said.
Example
We leave on Friday — that is, the fifteenth of June.
The plan needs to be cost-effective, that is to say, it must not cost more than it saves.