What is Uncle Block?

An uncled block is a block on the Ethereum network that is discarded because two blocks were mined at nearly the same time and only one can be validated and become part of the ledger. An Ethereum uncle block is similar to a Bitcoin orphan block. However, the two occur on different networks. Further, miners who generate uncle blocks on Ethereum are rewarded in ether (ETH), while miners who mine orphan blocks on the Bitcoin network are not rewarded in bitcoin (BTC).