Interchange reimbursement fee (IRF) is the formal name Visa uses for interchange, the fee that the merchant's bank pays to the card issuer on each card transaction. Visa publishes its rate schedules under this heading, and the term appears in acquirer pricing statements and in regulation of card fees. The main entry explains how interchange is set, collected and capped.
The word "reimbursement" reflects the networks' original justification: the fee was said to compensate issuers for the cost of processing, credit risk and fraud losses. Mastercard and most other networks simply say "interchange", so IRF and interchange refer to the same fee type, not two separate charges.
IRF is distinct from the network's own scheme fees and from the acquirer's markup; together these make up the merchant discount rate. Merchants on interchange++ pricing see the IRF passed through at cost. Current rates are listed in the Visa interchange rates table entry.