noun
hot-water tap; hot spring
Refers to a tap or spout for hot water, or by extension the hot spring itself. The 'hot spring' sense is less common and may be context-dependent.
旅館の湯口から温泉が出ている。
Hot spring water is flowing from the tap at the inn.
この湯口は熱いので気をつけてください。
This hot-water tap is hot, so please be careful.