Agent Operations
Coverage Gap
Also: monitoring blind spot
An action or stretch of activity that a monitor never sees, so it cannot be caught however good the monitor is.
In more detail
A monitor with strong detection on most traffic and none on the rest has a blind spot that does not show up in its own accuracy numbers. The useful figure is the denominator: how much of what your agents do is visible at all. Cross-check what ran against what was monitored.