When the transition probabilities of a Markov process are time-invariant. That is, for times s ≤ t in the time domain T, and any state x and any set A in the state space, Pr{X(t) ∈ A|X(s) = x} = Pr{X(t − s) ∈ A|X(0) = xv}. Markov chains; Markov processes.