시스템의 확률 분포가 시간이 지나도 변하지 않는 것을 의미 Stationary processIn mathematics and statistics, a stationary process (or a strict/strictly stationary process or strong/strongly stationary process) is a stochastic process whose unconditional joint probability distribution does not change when shifted in time. Consequently, parameters such as mean and variance also do not change over time.https://en.wikipedia.org/wiki/Stationary_process
