Pump and dump

Pump and dump is when someone buys a lot of a certain stock or crypto currency, and makes other people think that it's a really good stock to buy so they buy it too. Then, after the stock or crypto has gone up in price, the person who initially bought it sells all of their stocks/coins, making a big profit. This usually harms the other people who bought in because after the person dumps their stocks/coins, the stock/crypto goes back down in price.