Mempool

The mempool, short for memory pool, is the waiting room each node keeps for transactions that have been broadcast but not yet included in a block. When a wallet signs and sends a transaction, nodes check its basic validity, store it in their mempool and relay it to peers. Block producers then choose which pending transactions to include, usually preferring those offering higher fees. Because every node keeps its own copy, there is no single canonical mempool, and a transaction can be visible on one node and unknown on another. Analysts watch mempool size and pending fee levels to describe how congested a network is at a given moment. Pending transactions can be replaced or dropped before they confirm.