Interchange
The portion of a card fee that goes from the acquirer to the issuer, set by the scheme rather than by either party. It is the floor under any rate, which is why no provider can price below it and why a rate depends on which cards a merchant actually takes.
Why it matters to a merchant
The part of the cost no acquirer sets and none can waive, which is why the same merchant is quoted differently for a local debit card and a foreign credit card. Knowing that a floor exists is what makes an implausibly low quote recognisable as implausible.
Where this comes up
Pages on this site that deal with this in context:
Related terms
In this section: What it costs, and what gets measured