The mempool is the place your transactions go after you submit them but before they're officially confirmed on the blockchain. So in other words when you send a tx and get a "transaction pending" message, your transaction is in the mempool

Mempool stands for "memory pool" and it's basically just a temporary holding zone. Blockchains are peer to peer network, so when you send a tx it's messaged to all other nodes on the network and temporarily stored in the mempool. Miners or validators then pick txs out of the mempool and order them to form a block. Once a tx is confirmed in a block it's removed from the mempool

Miners typically order the txs from highest to lowest fees and choose the txs with the highest fees (they're incentivized to do this since they keep the fees if they win the block), but could really order the txs any way they want 

This is where MEV comes into play. For certain DeFi txs validators can pocket a profit for themselves by ordering the txs in an unexpected way

Interesting insight into how transactions are handled in the mempool and how miners prioritize them based on fees. MEV definitely adds another layer of complexity to the process. Thanks for breaking it down!