A rug pull is a scam variant in crypto where the team behind the coin intensively promotes the project and tries to drive up the price only to dump all their coins at once on the order book or by removing all liquidity in case of a DEX. Just like a literal rug pull where a rug is pulled out from under your feet, and you fall, the price of the coins also collapses. This is then clearly visible on the chart with a large red candle.