Wash trading
Also: fake volume
Wash trading is when one person or group buys and sells the same token between their own wallets. The price barely changes while the volume and trade count go up. On a DEX all it takes is a bot and a few dozen wallets, and the only cost is fees.
Why bother? Aggregators and “trending” lists weigh volume and trade count, so fake activity pushes a token up the rankings and draws in real buyers. High volume also looks like proof of liquidity and interest. That is why volume alone says little. Compare it with the number of unique wallets, the pool's liquidity and whether trades have similar sizes and timing.