A valid block which is not included in the current longest blockchain and thus does not contribute to the consensus protocol.
An orphan block is a valid block in a blockchain that is not included in the current longest chain. These blocks are fully valid and verified, they simply are not on the main chain. In blockchain networks like Bitcoin and Bitcoin Cash, orphan blocks represent a natural occurrence in the decentralized mining process, reflecting how consensus is achieved even with competing valid solutions.
"When two miners solve a block at nearly the same time, it might be that some nodes in the network receive one block first and others receive the other block first. Both blocks are added to the blockchain, but eventually one block becomes an orphan."
Orphan blocks occur when two miners produce blocks at similar times or when an attacker attempts to reverse a transaction. The network will only adopt one branch, and the block that is not selected becomes an orphan block. Networks with faster block times, like Bitcoin Cash with its 10-minute target, experience orphan blocks as a regular part of operation. The probability increases during network congestion or when there are propagation delays between mining nodes.
"If two miners solve a block at the same time, the network might be split on which one to add to the blockchain. The tie is broken when the next block is solved, effectively orphaning the other block."
Miners of an orphan block lose the block reward and the transaction fees they would have earned. It's as if their work never happened, even though the block they solved is just as valid as any other block. In some blockchain implementations like Bitcoin Cash, orphaned blocks might still receive partial compensation through protocols like GHOST (Greedy Heaviest Observed Subtree), which acknowledges the security contribution of orphaned blocks to the network.
"Mining an orphan block is unfortunate for the miner because even though they did the work to solve it, they receive no Bitcoin reward or transaction fees. Some networks have proposed systems to compensate miners for orphaned blocks to maintain mining incentives."
The probability of creating an orphan block is reduced by having a good connection to the Bitcoin network, as this ensures that you hear about blocks first. Mining pools help reduce orphan rates for individual miners by combining resources. Bitcoin Cash's improved block propagation techniques and more consistent block times help reduce the orphan rate compared to some other networks, making mining operations more predictable and efficient.
"Miners can reduce the chance of creating an orphan block by ensuring they have a reliable and fast connection to other nodes in the Bitcoin network. Larger operations often maintain direct connections to other major mining pools to minimize propagation delays."
All terms and definitions may update as the Cryptionary improves.