The thin slit shape that forms the gap between the labia majora of some pussies. Should not be used when the labia minora are visible (e.g. Danbooru post #5184055) or when the pussy is spread or gaping.
When skin tight clothing takes the shape of the cleft of venus, but the cleft itself is not visible, use cameltoe instead. The only time both can apply is when the clothing is see-through.
