Mempool
Also known as: memory pool, pending pool
The waiting area of unconfirmed transactions that have been broadcast to a blockchain network but not yet included in a block.
Definition
The mempool ("memory pool") is where broadcast transactions wait before a validator or miner includes them in a block. Higher fees typically get confirmed faster. For tax, the relevant timestamp is usually when a transaction is confirmed on-chain rather than when it entered the mempool, which matters when valuing proceeds or income at the right moment.
Example
Your transfer sits in the mempool for a few minutes during congestion; the confirmation time, not the broadcast time, is what you use for valuation.