运行 (yùn xíng) refers to the technical or mechanical operation of systems, programs, vehicles, or celestial bodies — how something functions or moves along its course. It differs from 运营 (yùn yíng), which is about managing a service or business (e.g., a subway line or a company), and from 运作 (yùn zuò), which focuses on the internal workings of an organization or system.