General systems theory is a set of related definitions, assumptions, and propositions which deal with reality as an integrated hierarchy of organizations of matter and energy. General systems behavior is concerned with a special subset of all systems, the living ones.
Even more basic to this presentation than the concept of "system" are the concepts of "space," "time," "matter," "energy," and "information," because the living systems which I shall discuss exist in space and are made of matter and energy organized by information.

p. 51; Opening paragraph - Living Systems: Basic Concepts (1969)