Glossary
Casper FFG
Ethereum's "Finality Gadget" — a BFT-style overlay on top of the LMD-GHOST fork-choice rule that finalizes checkpoints when two-thirds of stake attest across two consecutive epochs.
Casper FFG (Friendly Finality Gadget), originally proposed by Vitalik Buterin and Virgil Griffith in 2017, is the explicit- finality layer of Ethereum proof-of-stake. Validators submit "FFG votes" linking source and target checkpoints (epoch boundaries); when two-thirds of total stake vote for the same target across two consecutive epochs, the target is finalized.
The combination of Casper FFG (finality) and LMD-GHOST (fork choice within an epoch) gives Ethereum its hybrid finality model: fast block-by-block propagation with explicit finalized checkpoints every ~13 minutes.