The phrase "outer perimeter" refers to the outer boundary or edge of a defined area or space. It represents the outermost limits or boundaries of something. Full definition
«Individuals determined to be carrying firearms will not be allowed past a predetermined outer perimeter checkpoint, regardless of whether they possess a ticket to the event,» Holtzclaw said. (sun-sentinel.com)
The Secret Service said in a statement that the individual, whom it did not identify, was arrested on the south grounds without further incident after climbing an outer perimeter fence near the Treasury Department and East Executive Avenue at about 11:38 p.m. Friday. (fortune.com)
«At the end there is always an outer perimeter at which the security measures are never present,» says Bennet Waters, a counterterrorism expert at the Chertoff Group who served in the Department of Homeland Security. (fortune.com)