A referral link is a unique UR used by customers in referral programs to promote a company's brand and products. Customers enrol in a referral program, are given the referral link by the vendor, and then can use that link to drive traffic and sales to the vendor. The customer gets a cut of profit made from traffic to the link.
The payout partners receive for generating leads and revenues. It's almost always monetary, but can occasionally take the form of leads, giveaways, or marketing funds.