PII includes names, emails, phone numbers, addresses, payment details, and sometimes IPs or device identifiers. It requires careful storage, access control, logging, and deletion policies.
ELI5
Think of PII as the lock and rules that keep people and data safe. Personally identifiable information: data that can identify a person.
In practice
Use it when a workflow touches secrets, permissions, user data, payments, or untrusted input. In practice, define the owner, input, output, and failure mode before you rely on it.