Glossary
Attestation
A signed vote from an Ethereum validator on the current head of the chain and the most recent justified checkpoint — the building block of PoS finality.
In Ethereum PoS, every validator is assigned to a committee that attests once per epoch. An attestation is a signed message containing the validator's view of the chain head and the most recent justified checkpoint.
Attestations are aggregated (via BLS signatures) and posted on-chain. When two-thirds of stake attest to the same checkpoint across two consecutive epochs, that checkpoint is finalized — and reverting it requires a slashable supermajority attack.