Social proof is a phenomenon where people follow and copy the actions of others in order to display accepted or correct behaviour, based on the idea of normative social influence.
Social proof in a marketing context is evidence that other people have purchased and found value in a product or service offered by a business. Because people are more likely to purchase a product that others are already purchasing (the bandwagon effect), social proof can be a way to increase conversions by showing customers how popular a product or service is.
On the web, social proof can take many forms including customer testimonials and product reviews, customer lists and quantifiable data (“Over 50,000 downloads!”). All of these different tactics help build trust, convey value and improve conversions.