Although many definitions have been proposed by various SE groups, I see little to be gained in comparison to standard dictionary1 definitions:
1) A complex unity formed of many often diverse parts subject to a common plan or serving a common purpose;
2) An aggregation or assemblage of objects joined in regular interaction or interdependence: a set of units combined by nature or art2 to form an integral, organic, or organized whole: an orderly working totality: a coherent unification.
Or, we can simply call it the dingus, and be done with it.
Footnotes