1. that is to say;
(как поправка, уточнение) i (you, etc. ) mean;
~ вы ошиблись you mean, you made a mistake;
2. (выражает удивление) what do you mean?;
~, как - не знаешь? what do you mean, you don`t know?
that is, i.e., that is to say, in other words