This is the 16194th most frequent Korean word.
불허된
"불허된" means "not permitted" or "prohibited."
In this sentence, the word '불허된' describes a zone that has been officially prohibited for access.
그 지역은 불허된 구역이라 들어갈 수 없습니다.
That area is a prohibited zone, so entering it is not allowed.
Here, '불허된' modifies '물건' (items), indicating that the items mentioned are prohibited from being brought in.
불허된 물건을 반입하는 것은 엄격히 금지되어 있습니다.
Bringing prohibited items is strictly forbidden.
In this case, '불허된' describes '행동' (actions), signifying actions that are not allowed.