Strong consistency
Every reader sees the latest write immediately, regardless of which replica they hit. Requires coordination — more expensive and may block under partition.
Umbrella term including linearizability (single-object) and serializability (multi-object transactions). Powers Postgres single-node, Google Spanner (with TrueTime), CockroachDB, FoundationDB. CP in CAP — rather block than serve inconsistent data under network partition. Price in performance: extra round trips for consensus (Raft/Paxos).