This is the 5964th most frequent Korean word.
산악
Mountainous or related to mountains.
Here, '산악' depicts 'mountainous' emphasizing the nature of the terrain.
산악 구역에는 특별한 장비가 필요합니다.
Special equipment is needed in mountainous areas.
In this context, '산악' relates to mountain activities, especially as part of a group or club.
산악 동호회에서 등산을 매주 계획합니다.
The mountain climbing club plans hikes weekly.
산악 in this sentence describes 'mountain' as an adjective specifying the type of bicycle.