Uncle blocks
An uncle block is the same as a stale block but when referring to the Ethereum blockchain. Because the Ethereum blockchain processes blocks faster than the Bitcoin blockchain, it has higher chances of two valid blocks being broadcasted simultaneously, often referred to as the ‘uncle rate’. As more uncle blocks are created, to keep miners motivated the Ethereum ecosystem also provides a partial compensation for uncle blocks. Just like stale blocks though, they are not included in the original blockchain, therefore the uncle blocks transactions are not valid.