The Chinese word 出轨 (chūguǐ) is a compound formed through metaphorical extension: literally, it combines 出 (chū), meaning "to go out" or "exit", with 轨 (guǐ), meaning "rail" or "track", to create the literal image of a train derailing or leaving its tracks. This concrete meaning is then applied metaphorically to human behavior, primarily describing a person in a committed relationship who strays or "goes off the track" of fidelity by engaging in an extramarital or unfaithful affair. Thus, its formation exemplifies a common process in Chinese where a vivid literal compound acquires a widely understood abstract, social meaning.