In PoS systems, nodes need a recent finalized state to avoid certain long-range attacks.
Because validators can change over time without expending external work, PoS nodes rely on periodic finalized checkpoints from honest sources. Syncing from genesis without such context can expose nodes to long-range attacks.
"A new node bootstraps from a recent finalized checkpoint provided by multiple trusted sources to satisfy weak subjectivity."
All terms and definitions may update as the Cryptionary improves.