MEV (Maximal Extractable Value)
Profit extracted by manipulating transaction order in a block.
MEV: validators/sequencers decide tx order. Enables front-running, sandwich attacks, arbitrage. Hidden 'tax' on DeFi users. Annual ETH MEV: ~$700M. Mitigation: Flashbots Protect, private mempool.
In plain words
Whoever orders transactions in a block can profit by inserting themselves before yours. Common scheme: a bot sees your big DEX buy, buys ahead of you (price up), sells after you (profit). You pay more, the bot pockets the difference. A hidden DeFi 'tax'.
Example
Try buying 100 ETH for 300k USDC on Uniswap. Bot sees your tx, buys 50 ETH first (price up), sells after yours (profit). You paid 1% more, bot made $3000. Sandwich.
Also known as: MEV, front-running, sandwich attack