The word 圈子 (quānzi) is formed through a direct and vivid metaphorical extension. It combines the character 圈, meaning "circle" or "to encircle", with the common nominal suffix 子. The formation conceptually takes the physical shape of a circle, a bounded, continuous line enclosing a shared space, and applies it to the abstract social concept of a group. This creates the meaning of a "social circle", visually conveying the idea of people being figuratively "encircled" together by common interests, relationships, or affiliations, thus defining an inside and an outside.