ERGODIC

(l) of or relating to a process in which a sequence or sizable sample is equally representative of the whole (as in regard to a statistical parameter); (2) involving or relating to the probability that any state will recur, especially having zero probability that any state will never recur. (WEBSTER'S DICTIONARY)

A collection of systems forms an ergodic ensemble if the modes of behavior found in any one system from time to time resemble its behavior at other temporal periods and if the behavior of any other system when chosen at random also is like the one system. We do not require identical performance, only quite similar time averages and number averages. (If you cannot tell one youth from another or one adult from another, they belong to an ergodic ensemble.) In an ergodic population, any single individual is representative of the entire population. The salient characteristics of this individual are essentially identical with any other member of the group. (Iberall)