This is the 5235th most frequent Russian word.
оборонный
Defensive.
Here, "оборонный" describes a factory as related to defense, specifically producing equipment or goods for national defense purposes.
Оборонный завод работает круглосуточно.
The defense factory operates around the clock.
In this instance, "оборонный" relates to strategy, specifically one aimed at defense and protection.
В области разработали новую оборонную стратегию.
In the region, a new defense strategy was developed.
The term "оборонный" qualifies structures, indicating their purpose for military or protective defense.