Block finality refers to the point at which a block of transactions is considered permanent and cannot be altered or reversed. Once a block achieves finality, the transactions within it are securely added to the blockchain, ensuring that they are valid and irreversible.

In many blockchains, finality is reached through different consensus mechanisms. For instance, in Proof of Work systems, finality is often achieved when a block has a certain number of subsequent blocks built on top of it, making it increasingly difficult to change.

In contrast, protocols using Proof of Stake may utilize specific algorithms to arrive at a consensus where a block becomes final after a designated number of validators confirm it.

The importance of block finality lies in its role in securing transactions and maintaining trust in the system. It prevents double-spending and enhances the reliability of the network, giving users confidence that their transactions are permanently recorded and cannot be tampered with.