This background chapter analyzes the terms and the theory smart city. It explores smart city terminology, including several adjectives that have been applied during the smart city history and shows this evolution timeline following critical milestones that affected it. Moreover, it defines smart city with evidence from the international standards (ISO, ITU etc.) while it proposes a holistic definition that is based on the combination of widely adopted literature evidence and of official standardized approaches. Finally, it presents the conceptual and physical architectures of smart city to clarify the corresponding context and ecosystem.