From That is | Define That is at Dictionary.com

that is, (by way of explanation, clarification, or an example); more accurately:
I read the book, that is, I read most of it.
I believe his account of the story, that is to say, I have no reason to doubt it.
Literal and exactly the same.

Also it can be the question:
- То есть?
This means that you require more explanation for the previous phrase.