Orphan Block
Also: stale block
mining · intermediate
A valid block that loses a race — another miner found a block at the same height and the network built on the other one.
When two miners find a valid block at nearly the same time, the network briefly forks. Some nodes see block A first; others see block B. Each set builds on what it has. The fork resolves when the next block extends one of the chains — the losing block is "orphaned" and its transactions return to the mempool.
Orphans are not failures of consensus, they're how consensus handles propagation delay. They happen on roughly 1–2% of blocks; faster block-propagation protocols (Compact Blocks, FIBRE relay network) have reduced this from ~5% in early years.
The miner of an orphan loses the block subsidy entirely — six confirmations means a block's not finalized until others build on top. This is one of the economic forces keeping block intervals at ~10 minutes: shorter intervals would mean more orphans, more wasted work, weaker security per joule.