Glossary

Mempool

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The mempool (memory pool) is a smaller database of unconfirmed or pending transactions which every node keeps. When a transaction is confirmed by being included in a block, it is removed from the mempool. Nodes share mempool data by relaying signed transactions to each other, but there is no single mempool and few if any nodes keep the entire mempool. Miners draw transactions from the mempool to include in their blocks.

Related Terms
Transaction
A transaction exists as a record of the transfer of bitcoin from one address to another. All transactions are recorded in blocks on the blockchain.
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Confirmation
A Bitcoin transaction is confirmed when it has been included in a block. Before then, it is simply pending, and exists only in the mempool. After a transaction is added to a block, each subsequent block is an added confirmation for the transaction, indicating a higher level of security.
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Bitcoin Transaction Fee
All Bitcoin transactions must pay a fee to be included in the blockchain. The fee is paid to the miners. The higher the fee, the faster the transaction will be confirmed. Fees are measured based on the data size of the transaction.
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