Orphan Block

Orphan block is a term used for a block that does not belong to the currently accepted blockchain chain. The exact use of the term varies between protocols and implementations.

A typical situation occurs when multiple blocks compete for the same position in the chain. After the competition is resolved by the consensus rules, one continuation is accepted and an alternative block may no longer belong to the active history.

Technical documentation may distinguish an orphan block from a stale block, while some discussions use the terms more loosely. The exact meaning should therefore be interpreted according to the relevant protocol.