A mempool is a node's local collection of valid or potentially valid transactions that have been received but have not yet been included in the blockchain.
In blockchain networks that use mempools, nodes validate incoming transactions against protocol rules and relay eligible transactions to peers. Block producers select transactions from the set they know about, often considering fees and other policy rules. Because nodes receive transactions at different times and can apply different local policies, there is not necessarily one globally identical mempool.
A mempool contains pending transactions known to a node. A confirmed transaction has been included in the ledger according to the network's consensus process.
Mempool conditions can affect transaction latency and fees, especially during congestion, and therefore matter for time-sensitive stablecoin payments.
A stablecoin transfer can remain pending in a node's mempool until a block producer includes it in a block.