The word bunker has two main meanings:

1. A heavily protected underground shelter built to keep people safe during attacks or disasters. During World War II, families in London sheltered in backyard bunkers during German bombing raids. Modern military bunkers have thick concrete walls and can withstand enormous explosions. Some bunkers built during the Cold War could protect people from nuclear weapons. The word suggests a fortress-like refuge, dug into the earth where danger can't easily reach. Leaders sometimes command operations from secure command bunkers deep underground.
2. A sand trap or depression on a golf course, usually filled with sand. Golf bunkers make the game more challenging by creating obstacles between the tee and the hole. If your ball lands in a bunker, you'll need to use careful technique to hit it out onto the grass. Links-style golf courses in Scotland, where the game originated, feature natural bunkers shaped by wind and weather over centuries.