The contrast is between the literal meaning of what is said and what is meant-

Verbal irony is a figure of speech.
The speaker intends to be understood as meaning something that contrasts with the literal or usual meaning of what he says.
The different sorts of discrepancy between the meaning of what is said and what is in fact on the particular occasion meant with it give rise to different kinds of verbal irony.

The verbal irony arises from a sophisticated or resigned awareness of the contrast between what is and what ought to be and expresses a controlled pathos without sentimentality.

Source: Britannica and KSU Doc.