What Is “Finality” in a PoS Consensus Mechanism?

Finality in a PoS consensus mechanism is the point at which a transaction or block is guaranteed to be irreversible, even if a malicious validator attempts to reorganize the chain. Unlike PoW, which has "probabilistic finality" (the chance of re-org decreases with each block), many PoS systems achieve "economic finality" after a certain period or a supermajority vote.

Once finality is reached, any attempt to revert the block would result in the slasher of the attacker's stake, making the reversal prohibitively expensive.