A mempool, short for ‘memory pool’, serves as a temporary storage area for pending transactions that have been broadcast but not yet confirmed by miners or validators.
On Bitcoin, before a transaction can be added to a block and recorded on the blockchain, it needs to be validated by miners. Transactions in the mempool are prioritised based on factors like transaction fees and transaction size. Miners typically prioritise transactions with higher fees, and users can adjust the transaction fee to influence the priority of their transactions.
The size of the mempool can fluctuate based on network activity. During times of high demand, such as when there are many transactions waiting to be processed, the mempool size increases and network traffic becomes more congested. Once a miner includes a transaction in a block and successfully mines that block, the transaction is considered confirmed. It is then released from the mempool.