Type Definition sp_runtime::Justification

type Justification = Vec<u8>;

An abstraction over justification for a block's validity under a consensus algorithm.

Essentially a finality proof. The exact formulation will vary between consensus algorithms. In the case where there are multiple valid proofs, inclusion within the block itself would allow swapping justifications to change the block's hash (and thus fork the chain). Sending a Justification alongside a block instead bypasses this problem.