PII

Personally Identifiable Information: any data that can identify a specific individual, like name, email, SSN, or IP address. Must be encrypted and access-controlled.

PII is a intermediate-level concept that sits in the Data Governance & Compliance area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.

If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "PII" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.