system
System refers to the theory of autopoietic systems, i.e. self-created and self-organized entities who are actually a system-environment complex. What delineates a system is its operational closure which can be implemented in many ways (a membrane, for a biological cell, a set of rules for a social group).
Some systems may seem artificially created, and though they do possess an operational closure, this will only be "operational" inasmuch the system has some relevance. For instance, the borders of a country, though they are drawn by convention (or through war...), become truly viable if they correspond to some social, cultural, ethnic substrate and inasmuch they can establish sustainable structural and functional couplings with their environment.