In probability theory and statistics, a zero-order process is a stochastic process in which each observation is independent of all previous observations. For example, a zero-order process in marketing would be one in which the brands purchased next do not depend on the brands purchased before, implying a fixed probability of purchase since it is zero order in regards to probability.
References Ward, Scott; Robertson, Thomas S. (1973). Consumer behavior: theoretical sources. Prentice-Hall. p. 536. ISBN 0131693913.