A DEX (decentralised exchange) lets users trade cryptoassets directly from their own wallets, using smart contracts instead of a centralised company holding custody of funds. Many DEXs use an automated market maker model, pricing trades against a liquidity pool rather than matching individual buy and sell orders.
Because there's no central operator vetting what's listed, a DEX typically has little to no screening of the assets available to trade — which means genuine due diligence on any specific token is entirely down to the user.