Bullet Proof
Adjective · Slang & Abbreviations
Definitions
A casual way to say something seems extremely robust, reliable, or hard to break. In engineering slang, it is often used optimistically, sometimes more optimistically than the evidence really supports.
In plain English: Very robust and hard to break.
Example: "The rollback process looked bullet proof in rehearsal, but production taught them that one missing secret rotation path could still derail the plan."