In the mathematics of probability, a stochastic process is a random function. In the most common applications, the domain over which the function is defined is a time interval (a stochastic process of this kind is called a time series in applications) or a region of space (a stochastic process being called a random field).
Familiar examples of processes modeled as stochastic time series include stock market and exchange rate fluctuationsHowever, sometimes the market is also modelled as Brownian Motion, Continuous time Markov Process(Random Walk) or a Gauss-markov Process. Most of the time the time series model will fit however.