An orphan block refers to a block in a blockchain that is not included in the main chain. This occurs when two blocks are mined nearly simultaneously, leading to a temporary split. Each block has its own set of transactions, but only one can be accepted into the main chain.When miners find a new block, they broadcast it to the network. If another miner finds a block at the same time, both may be valid, but only one will eventually be confirmed as part of the main chain. The blockchain protocol resolves this by accepting the longest chain as the valid one.Once a block is orphaned, the transactions contained within it are not lost; they can be re-included in future blocks. Orphan blocks serve as a reminder of the decentralized nature of the system, where multiple chains can exist temporarily until the network reaches consensus on the correct one. While orphan blocks are a normal part of blockchain functioning, excessive orphaning can indicate issues like network instability or low hash rates.