Fetching details from the dictionary...

(the) negative (e.g. pole)
yin (in Chinese divination)
hidden place; unseen part; private location
電池の陰と陽を間違えないで。
Don't mix up the negative and positive on the battery.
東洋思想では陰と陽が対をなす。
In Eastern philosophy, yin and yang form a pair.
陰の気が強まると体調を崩しやすい。
When negative energy strengthens, it's easy to get sick.