exchangeability

In statistics, an exchangeable sequence of random variables (also sometimes interchangeable) is a sequence such that future samples behave like earlier samples, meaning formally that any order (of a finite number of samples) is equally likely. This formalizes the notion of "the future being predictable on the basis of past experience." It is closely related to the use of independent and identically-distributed random variables in statistical models. Exchangeable sequences of random variables arise in cases of simple random sampling.