Recently, in collaborative systems, several terms have been frequently used, such as “System-of-systems”, “Mega-systems”, “Holonic-systems” and “Autonomic systems”, although, despite their frequent usage, there is a remarkable lack of consensus on their precise definitions. This work aims to clear up any confusion about the fundamental characteristics of these systems, how to distinguish them from classical systems, and how their evolution differs from other systems, even if there is less agreement on these points. We provide definitions, a simplified taxonomy, and an essential set of design problems and principles. This paper also discusses the necessity of recognizing categories in system design, as well as some of the potential issues raised by misclassification.