A memory pool, or mempool for short, is a node’s mechanism for storing unconfirmed transactions. It acts as a waiting room for transactions that have yet to be included in a block. Miners choose which transactions to put into the next block based on the transaction fee each transaction pays. This creates a priority list within the mempool of the transactions that are closest to being confirmed next. The sharing of transactions propagate within the mempool from a node to its peers until the transaction is widely recognized by nodes.