Definition
The mempool (memory pool) is a temporary data structure maintained by a blockchain node that stores valid, unconfirmed transactions waiting to be included in a block. It acts as a holding area where transactions are organized, filtered, and prioritized according to network rules and fee levels until block producers select them for on-chain inclusion.
In Simple Terms
The mempool is a waiting room inside each node where new transactions sit before they are written into the blockchain. Once a transaction is broadcast and accepted as valid, it stays in the mempool until a block creator picks it up and it becomes part of the permanent on-chain record.
Context and Usage
The term mempool is commonly used when discussing transaction congestion, gas fee dynamics, and the visibility of pending on-chain activity. Different nodes may have slightly different mempools depending on their policies and what transactions they have received. Observing mempool contents is central to topics like MEV, transaction ordering, and estimating how quickly a transaction might transition from pending to confirmed.