Stationaire

Stationaire is a term used in several languages, notably French, to describe things that do not move or do not change with time. In English, the closest form is stationary. The word derives from Latin statio, the act of standing or a fixed position, and in technical usage signals a state, property, or phase that remains constant under specified conditions.

In physics and mathematics, stationary concepts include stationary states in quantum mechanics, stationary distributions in stochastic processes, and stationary points where a function’s derivative is zero. A stationary process or time series has statistical properties that do not depend on time. Similarly, a stationary regime or state describes a system whose behavior is time-invariant after initial transients.

In chemistry and analytical methods, the stationary phase is the fixed material or liquid through which a mobile phase moves during chromatography, enabling separation of components. In engineering and systems theory, steady-state or stationary analysis describes the long-term behavior of a system after transients have died out.

Outside pure science, the term can refer to objects or locations at rest relative to a frame of reference, or to broader notions of constancy. The concept contrasts with non-stationary or transient phenomena, which change or move over time. In multilingual technical literature, stationaire or stationaire-related spellings appear as equivalents of the English stationary, depending on language and domain. See also stationary, stationary distribution, stationary phase, and non-stationary.