Finality
Plain English
When a transaction is considered permanently settled and cannot be reversed. Different blockchains achieve finality differently - Bitcoin takes ~1 hour (6 confirmations), Solana achieves finality in ~13 seconds. Think of it as when a bank transfer is fully complete and cannot be reversed.
Technical
The assurance that a transaction is irreversible and permanently included in the blockchain. Types: probabilistic finality (confidence increases with confirmations, used in PoW) and deterministic finality (absolute guarantee after specific conditions, used in some PoS systems). Solana achieves optimistic confirmation in ~400ms and absolute finality after 32 slots.