Finality

Finality is the point at which a confirmed transaction can no longer be reversed by a reorganisation of the chain. Until finality is reached, a block can in principle be replaced by a competing one, and the payment inside it would disappear — which is why exchanges wait for a number of confirmations before crediting a deposit. Networks reach it differently: proof-of-stake designs can offer deterministic finality once a supermajority of validators has attested to a checkpoint, while proof-of-work chains only make reversal progressively more expensive. Layer-2 networks add a second dimension, because a transaction can look final on the rollup while its settlement on the base chain is still pending.