Orphan Block
A block that cannot currently extend a node's active chain, often because its parent is unknown or a competing branch lost the proof-of-work race.
- Also known as
- stale block
"Orphan" and "stale" are often used interchangeably, but they can describe different cases. An orphan block has an unknown parent from the receiving node's perspective; a stale block is valid but no longer belongs to the active chain after a competing branch accumulates more proof of work.
Competing blocks can arise when miners find valid blocks close together and different peers receive them in different orders. Nodes may temporarily follow different tips, then converge as one branch gains more accumulated work. Propagation delay matters relative to the network's block interval and can increase stale-block risk.
A miner cannot spend the coinbase reward from a stale Bitcoin or Bitcoin Cash block. Transactions from that block may already appear in the winning branch or return to mempools if they remain valid and unconfirmed. Bitcoin and Bitcoin Cash do not pay partial "uncle" or GHOST rewards for stale blocks.
Miners reduce avoidable stale work through fast block relay, reliable peer connections, current validation software, and by switching promptly to a chain with more work. Pools reduce an individual worker's reward variance, but they do not eliminate network-wide stale blocks.
Related terms
Explore connected entries beyond the alphabetical index.
Block
→A batch of valid transactions added to a blockchain, linked to the previous block by a cryptographic hash.
Proof of Work (PoW)
→A consensus mechanism that makes block production require verifiable computational work.
Miner
→A proof-of-work participant that builds or searches candidate blocks and earns revenue when an accepted block is found.
Confirmations
→The count of blocks confirming a transaction, usually including the block that first contains it.