The mempool (memory pool) is a waiting area where valid, unconfirmed transactions sit before being picked up by miners or validators and included in a block.
How the mempool works: Transaction is broadcast to network, nodes validate and add to their mempool, miners/validators select transactions (usually by fee), and selected transactions are included in next block.
Mempool congestion: High demand increases mempool size, transactions compete through higher fees, low-fee transactions may be stuck, and congestion visible through monitoring tools.
Mempool strategies: Monitor mempool for optimal fee timing, use RBF (Replace-By-Fee) for stuck transactions, and Layer 2 solutions avoid mempool congestion.