Definition
An orphan block is a valid block that was mined according to consensus rules but is excluded from the canonical blockchain because a competing chain segment with greater cumulative work or length was selected instead. It typically shares the same parent as the winning block at that height, becomes detached from the main chain during a reorganization, and its contained transactions are not recognized as confirmed in that chain state.
In Simple Terms
An orphan block is a block that followed all the rules but lost a race to be part of the main blockchain. Another block at the same height was accepted instead, so the orphan block and its transactions are left outside the official chain, even though the block itself is technically valid.
Context and Usage
The term orphan block is used when discussing chain selection, temporary forks, and the effects of network latency in proof-of-work systems. It appears in analyses of mining performance, block propagation, and security assumptions around finality and reorg depth. Orphan blocks are relevant to how nodes agree on a single canonical history and how difficulty and cumulative work influence that selection.