With interchange-plus pricing, your statement shows the actual interchange and card network fees on each sale, then the processor's markup as a percentage, a per-transaction fee or both. You see what the card system charges and what your processor keeps.
The main alternatives are tiered pricing, which sorts sales into buckets such as qualified and non-qualified, and flat-rate pricing, which charges one rate for everything. Both are simpler to read but make the markup harder to see.
Example: On $40,000 of monthly card sales with interchange averaging 1.80% ($720), a markup of 0.30% ($120) plus $0.10 on each of 800 transactions ($80) brings the total to $920. That is an effective rate of 2.30% before card network fees.
Compare processors on the markup, because the interchange on a given sale does not depend on which processor handles it.