Unknown Unknown
Noun Phrase · Slang & Abbreviations
Definitions
A risk or factor you do not even know exists yet, making it impossible to plan for directly. In engineering slang, unknown unknowns are why humility matters in ambitious rollouts.
In plain English: A risk you do not know about at all yet.
Example: "The team had planned carefully for known risks, but the outage still came from an unknown unknown in the vendor failover path."