Here is an explanation (not a definition) of what a metasystem is, given in the context of "metasystem transition:

http://pespmc1.vub.ac.be/MST.html

"Consider a system S of any kind. Suppose that there is a way to make some number of copies from it, possibly with variations. Suppose that these systems are united into a new system S' which has the systems of the S type as its subsystems, and includes also an additional mechanism which controls the behavior and production of the S-subsystems. Then we call S' a metasystem with respect to S, and the creation of S' a metasystem transition. As a result of consecutive metasystem transitions a multilevel structure of control arises, which allows complicated forms of behavior. We refer to the original system S as the scope of the MST, and to the number of integrated systems as its scale. The minimal scale of an MST is one. In this case there is no reproduction of the scope, but a control level still emerges, so it is a metasystem transition."

It was tempting at first to call a metasystem نظام مركب, but I realized that every system is نظام مركب, not just metasystems. So I thought perhaps متراكب might capture the additional complexity inherent in metasystems.