A source of truth is the authoritative record that teams use to keep facts consistent. In cybersecurity, it is the one place where incident details, asset data, identities, or reporting fields are considered correct until they are updated through a controlled process.
This matters because security work often involves many copies of the same information: tickets, logs, alerts, case notes, legal reports, and regulator filings. If each system drifts, responders may give conflicting answers, miss deadlines, or make bad decisions based on stale data. In an attack, the source of truth helps teams track what happened, what was affected, and what actions were taken. In defense, it supports reliable change control, incident reporting, and auditability. A strong source of truth is usually backed by clear ownership, version control, and access controls so the record stays accurate and trustworthy.