Wiktionary
adv. (context conjunctive English) in other words; that is to say. (non-gloss definition: Used to introduce a clarification or explanation)
WordNet
Usage examples of "that is".
Ganakari links directly to Spoltam, you foolish girl, and if you know not what place that is, then you are truly naive.
Mollock with the disdainful expression of a cat that is expected to step in, well, mud.
At least, that is what she had once overheard from a group of gossiping females attending the same festival as her.
In Italy, when passengers asked for all due speed, that is precisely what they received!
Even the private detectives she had attempted to hire all turned the job down flat, that is, once they learned for whom they would have been working.
For the first time he was being accorded the doffed hat that is the due of Heralds from their inferiors in the Order, and the grave nod of salutation from equals.