A pump-and-dump scheme is a type of scam where groups of scammers artificially inflate the price of a cryptocurrency or token that they have bought very cheaply. They do this through building hype on social media and forums, sometimes using popular influencers to spread the message. As more and more people buy the token, the price skyrockets until the scammers sell everything they have for a huge profit, thus creating a sudden influx of supply and crashing the price, leaving buyers with a low-value asset.