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Related to that is: that is to say
Also, that is to say. To explain more clearly, in other words, as in It's on the first floor, that is, at street level, or We're coming next month, that is to say, in November. [Early 1600s] Also see under that's.
that is (to say)
1 in other words: I’m between jobs at the moment; that’s to say unemployed. ♢ It cost him a week’s wages, that is, €300.
2 used to give more information or to correct what has already been said: She’s a housewife — when she’s not teaching English, that is. ♢ Let him explain it — if he can, that is. ♢ Nobody wants to do it. Nobody except me, that is.
To explain more clearly; in other words: on the first floor, that is, the floor at street level.