Conversion rate
Conversion rate is completions of a target action divided by the audience exposed to it — purchases per click, signups per visit. It converts attention into commerce and is the number affiliate and CPA maths stand on. Creator-driven conversion lags posts by days, so windows matter: same-day measurement systematically undercounts.
Worked example
500 link clicks producing 15 orders is a 3% click-to-order conversion rate.
Full context in the guides, or measure it yourself with the free tools.