Service and service systems concepts are fundamental constructs for the development of the emergent SSME, ITSM, and Service Oriented Software (SOS) knowledge streams. A diversified literature has provided a richness of findings, but at the same time, the lack of standardized conceptualizations is a source of confusion to IT practitioners and academics. Given this problematic situation, we pose that a systems approach is useful to address it. In this article, we review and synthesize key studies in these knowledge streams to design: (i) a framework to characterize both concepts under a system view and, (ii) harmonized definitions (e.g. identification of shared and essential properties) for such fundamental concepts. Our main contribution is scholastic, but we are confident that the posed conceptual artifacts can be further used to elaborate standardized definition for the IT service and IT service system constructs, as well as analysis tools for describe real service systems.