“Conversion rate” is the term marketers use to keep track of how many site visitors do something. The definition of "do something" is dependent on the marketing campaign being run. Affiliate program information, such as conversion rate, is essential to understand. If you're getting people to click through to the merchant site but none of them are buying anything (converting to customers) that doesn't benefit the merchant. Play with the wording, design, and layout of your pages and ads and find out which has the best conversion rate.