Couloir, a French term used in the mountainous regions to describe a steep and narrow gully. Synonyms for this word include gully, canyon, ravine, defile, and pass. Gully refers to a small narrow valley, while a canyon is a deep and narrow valley with steep sides. A ravine is a deep narrow valley with steep sides, usually formed by the action of running water. Defile is a narrow pass between mountainous areas, while pass is a low point in a mountain range that allows movement from one side to the other. Each of these words can be used interchangeably to describe a couloir in the mountains.