Markov chain
Markov chains can be discrete or continuous. Discrete Time Markov Chains are split up into discrete time steps, like t = 1, t = 2, t = 3, and so on. The probability that a chain will go from one state to another state depends only on the state that it's in right now. Continuous Time Markov Chains are chains where the time spent in each state is a real number. The amount of time the chain stays in a certain state is randomly picked from an exponential distribution, which basically means there's an average time a chain will stay in some state, plus or minus some random variation.