What is Mempool?
The mempool (memory pool) is the in-memory set of valid, broadcast-but-unconfirmed transactions each node maintains. Miners and validators pick transactions from their mempool — usually by fee rate — when building the next block.
Why Mempool matters
Understanding Mempool is part of building a solid mental model of how Bitcoin, blockchain and Web3 systems actually work. Concepts in the Bitcoin category sit at the foundation of the broader stack — get them right and the rest is far easier.
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Reading the definition is a start. ZeroToBlock teaches concepts like Mempool through hands-on, browser-based simulations. Build the mental model by actually using it:
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Related terms
- Transaction — A signed instruction that updates the blockchain state.
- Mining — Producing new blocks by performing Proof of Work.
- Fee Rate — Transaction fee per vbyte or per gas unit.
More bitcoin terms
- Address (Bitcoin / Crypto Address) — A public destination for receiving cryptocurrency.
- Block Header — The metadata at the top of each block.
- Block Reward — New coins paid to the miner of a block.
- Difficulty — A parameter that controls how hard it is to mine a block.
- Double Spend — Attempting to spend the same coin twice.
- Halving — The scheduled 50% cut in Bitcoin's block subsidy.
- Hash Rate — The total computational power securing the network.
- Nakamoto Consensus — Bitcoin's consensus rule: follow the chain with the most work.
Keep exploring
Continue with the full blockchain glossary — 136 terms in total — or read the developer blog and FAQ for deeper context.