A stochastic process is any process governed by the laws of probability: for example, the Brownian motion of the submicroscopic particles in a colloidal solution (see colloid). Most stochastics involve time. In the case of particles, the state of the system at a time t is a random variable, x(t). In mathematics, particularly statistics, a stochastic is a family of random variables. The price of a stock is often modeled as a stochastic process.