that is to say

US /ðæt ɪz tə seɪ/
UK /ðæt ɪz tə seɪ/
"that is to say" picture
1.

used to introduce a clarification or explanation of a preceding statement

:
He is a polyglot, that is to say, he speaks many languages.
The event is scheduled for next Tuesday, that is to say, October 26th.