Affiliate programmes are arrangements in which an online merchant website pays an affiliate website a commission for sending them leads (customers). Usually, there is a link on an affiliate site and when users click through, they are transferred to the merchant's website. The merchant will usually have a tracking mechanism to track how many leads or referrals are being directed through the affiliate link and can pay the affiliate a fee or commission accordingly.
Many online businesses benefit from recruiting affiliates to sell products or services online, but it can also be a cheap and effective marketing strategy.