Orphan blocks are valid blocks that have been excluded from the main chain. Since there are all these miners competing to mine the next block and they might both find solutions to the hash at a similar time. Only one of the blocks will be accepted into the Bitcoin blockchain. Ethereum uses something called the Ghost protocol to reward the miner who found the Orphan block, or uncle as it is called in Ethereum terminology, and a smaller portion of the block reward is also given to the miner who found the nephew or child of the uncle block. Orphan block is a confusing term because it can also refer to a block that went stale. This happens when the network first trusts a new block and then goes back on that trust and follows a new longest chain.