The additional lift in visits, conversions, or revenue directly caused by a marketing intervention, over and above what would have occurred organically.
This is the metric that separates real marketing impact from visits that would have happened anyway a campaign can drive plenty of visits and still have near-zero incrementality if most of those visitors were going to show up regardless, which is why incrementality testing (via a held-out control group) is considered more rigorous than simple attribution.
Further reading: Retail site selection · How offline attribution works
