In blockchain terms, the term orphan block refers to a block which is generated by mining, but is not included in a blockchain. Orphan blocks result when two or more miners create identical blocks, because only one can be added to the blockchain. The rejected block is referred to as an orphan block.
In the case of cryptocurrencies and other blockchain applications which use the proof of work model, preference is automatically given to the block created by the mining node which delivers higher hash power and subsequently processes larger numbers of transactions. In the case of blockchain applications based on the proof of stake model, preference is given to the block created by the mining node which holds the larger number of coins in its wallet.
Preferred blocks are recorded across the distributed ledger (the blockchain), while blocks generated simultaneously by other miners are revoked by the system and are not recorded on the distributed ledger. These non-preferred blocks become orphan blocks.