that is to say
US /ðæt ɪz tə seɪ/
UK /ðæt ɪz tə seɪ/

1.
c'est-à-dire, autrement dit
used to introduce a clarification or explanation of a preceding statement
:
•
He is a polyglot, that is to say, he speaks many languages.
Il est polyglotte, c'est-à-dire, il parle de nombreuses langues.
•
The event is scheduled for next Tuesday, that is to say, October 26th.
L'événement est prévu pour mardi prochain, c'est-à-dire le 26 octobre.