A "bunker" is a golf course hazard that is a hole or depression in the ground filled in with sand (or a similar material). Bunkers vary greatly in size and shape and depth. They are most commonly found serving as greenside hazards, but also often show up in fairways and alongside fairways.

In the vernacular, one might hear reference to a "grass bunker," a hollowed-out area or depression in which, rather than sand, there is simply more (often deeper) grass.

However, a "grass bunker" is not technically a bunker, because it is not a hazard under the rules. It's simply akin to rough.

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