Front-running

Front-running is when someone sees your transaction waiting to be confirmed and jumps in with their own trade first, using that advance knowledge to profit at your expense. It matters because blockchains publish pending transactions in a public queue before they finalize, so anyone watching can copy or exploit your move before it lands. On Ethereum, this shows up as MEV: a bot spots your large swap on Uniswap, buys the same token first to push the price up, lets your trade execute at the worse price, then sells for a quick profit. Traders guard against it by setting tight slippage limits or using private transaction relays like Flashbots Protect, which hide orders from public view until they're confirmed.