Refers to a fortified place or a secure base, often in a military or historical context.
The enemy holed up in their stronghold on the mountain.
base of operations; headquarters
Extended use for a place where someone or a group is based, such as a gang's hideout or a company's main office.
This is their base of operations.
Formed from 根, “root or base,” and 城, “castle.” It originally denoted a principal castle serving as the base of a territory, and later any stronghold or operational base.