Yin is the English spelling of Chinese 陰. In Chinese thought it names one of the two forces that together make up everything: yin is the quiet, dark, cool, still, receiving, inward side, and yang is the bright, warm, active, moving, outward side. English books usually describe yin as "female" and "negative", but be careful — "negative" here does not mean bad, and yin is not weakness. It is the other half of a pair, and the whole idea is that neither can exist alone and each is already turning into the other. In everyday English the pair almost always travels together as "yin and yang", used loosely to mean two opposite things that balance each other: "They are the yin and yang of the office — she plans, he improvises." People also talk about "the yin and yang of" a situation to mean its two sides. On its own, yin appears mostly in writing about Chinese medicine, feng shui and philosophy — "a yin food", "yin energy" — and in yoga, where "yin yoga" is the slow kind with long, still poses. It has no plural and takes no a: you say "more yin", not "a yin". Separately, in Scottish speech "yin" is a completely different word meaning "one" — "the wee yin", the little one.