Finality

Finality is the point at which a transaction on a blockchain is considered permanent and can't be reversed or rewritten. It matters to a reader because it determines how long you should wait before treating a payment or trade as safe from being undone by a chain reorganization. On Bitcoin, finality is probabilistic: most exchanges wait for 6 confirmations, roughly an hour, before crediting a large deposit. Ethereum, since its move to proof of stake, has "checkpoint" finality, where blocks become mathematically irreversible after about 12-15 minutes once two-thirds of validators attest to them. Some newer chains aim for near-instant finality, settling in seconds. The tradeoff is usually speed versus certainty: faster finality often means trusting a smaller set of validators.