What Is the Difference between “Justified” and “Finalized” Blocks?

A block is considered "justified" when two-thirds of the validators have attested to it, indicating strong agreement. A block becomes "finalized" when the subsequent block is also justified.

Finalization requires two consecutive epochs (a period of 6.4 minutes) of two-thirds supermajority attestations. Finalized blocks are considered irreversible, meaning they cannot be reverted without a massive, coordinated, and economically suicidal attack.