Finality

The point at which a transaction or block is considered irreversible. Bitcoin achieves probabilistic finality: after six confirmations, reverting a transaction would require redoing more proof-of-work than the network produces in that time. Ethereum's proof-of-stake uses Casper FFG checkpointing to reach economic finality after two epochs (~13 minutes), after which reversion would require slashing at least one-third of staked ETH.