庭

The word refers primarily to the outdoor space adjacent to a residence. In a Japanese context, this can range from a simple yard with grass and soil to a highly stylized "Japanese garden" (nihon teien), which is designed for contemplation and aesthetic harmony rather than just utility.

When used metaphorically, it describes a person's area of expertise, a field where they possess superior knowledge, or a physical/social space where they feel completely in control and confident. This is similar to the English concept of "one's own turf" or "domain."

It is important to distinguish "niwa" from "koen" (public park). While both involve greenery, "niwa" almost always implies a sense of ownership or a specific attachment to a building or household. In the metaphorical sense, it is often used in competitive or professional contexts to indicate that someone is operating within their strongest specialty.