Mempool
The waiting room of unconfirmed transactions, where fee bidding decides who gets into the next block.
The mempool (memory pool) is each node’s queue of valid transactions awaiting inclusion in a block. When blocks are full, miners and validators pick the highest fee-payers first — the mempool is the open auction for scarce blockspace, and why fees spike during congestion.
Watching it is practical: sites like mempool.space show live congestion and what fee gets confirmed in the next block versus in hours — useful before sending anything urgent. On smart-contract chains, the mempool’s transparency also enables MEV: bots reading pending transactions to trade around them.