Orphan blocks are those that were mined concurrently with another block but were rejected by the network. The majority of the time, this occurs because the network does not recognize that block as the longest fork due to insufficient blocks being generated from it. Orphan blocks are removed from the Bitcoin blockchain, although they might be useful to other blockchains for other reasons.
It is possible for two miners to solve valid blocks simultaneously. The network uses both blocks until one chain has more validated blocks than the other. The blocks in the shorter chain are then abandoned as orphans.
Orphan blocks frequently appear in distributed blockchains like those used by Bitcoin and Ethereum.
