For what it's worth, when I asked the question you mention, I had in mind a position like this (black to move):
[FEN "rnbq1rk1/pppp1ppp/4pn2/8/1bPP4/2NBP3/PP3PPP/R1BQK1NR b KQ - 0 1"]
The question regarded whether black should push the c-pawn or the d-pawn, or push neither, or prepare something before pushing. Of course, the question did not regard this particular position, nor was it specific to the opening or to the midgame; but it regarded rather the principles that guide the black player to open files from such positions generally.
Update: In response to helpful comments: I do not know for sure how the term pawn break is conventionally defined. I should defer to @Andrew's and @TomAu's answers. Nevertheless, pawn break is the term I seem to have heard opponents use for the act of pushing a pawn with the intent to force a file open.
Thus, to answer the question directly, to the extent to which my terminology is correct, d7-d5 would constitute a pawn break in the position diagrammed, because the likely and intended effect of such a pawn move would be to open, or half-open, one or more files by trading off the pawns that occupy the files.