Affiliate marketing is a type of online marketing where individuals or companies promote other people's or company's products, and earn a commission for every sale made through their unique referral link. It is a performance-based marketing strategy where the affiliate promotes the product through various online channels such as blogs, social media, or email marketing, and earns a percentage of the revenue when a sale is made. It is a win-win situation for both the affiliate and the business, as the affiliate can earn passive income while the business can increase its sales and brand awareness.