This paper proposes a comprehensive definition of systems thinking, emphasizing its importance in various disciplines and educational contexts. The authors, Ross D. Arnold and Jon P. Wade, derived the definition from a review of the literature and the application of systems thinking to itself. They argue that many existing definitions of systems thinking are incomplete or overly simplistic, often failing to capture the systemic nature of the concept. The proposed definition integrates key components of systems thinking as a system, including its goal, elements, and interconnections. The definition is tested against a System Test and three widely accepted system archetypes, confirming its fidelity. The paper highlights the need for a complete and widely accepted definition of systems thinking to enhance its educational and practical applications. The proposed definition includes elements such as recognizing interconnections, understanding feedback loops, differentiating types of stocks and flows, and modeling systems conceptually. This definition aims to provide a robust framework for teaching and applying systems thinking in various fields.This paper proposes a comprehensive definition of systems thinking, emphasizing its importance in various disciplines and educational contexts. The authors, Ross D. Arnold and Jon P. Wade, derived the definition from a review of the literature and the application of systems thinking to itself. They argue that many existing definitions of systems thinking are incomplete or overly simplistic, often failing to capture the systemic nature of the concept. The proposed definition integrates key components of systems thinking as a system, including its goal, elements, and interconnections. The definition is tested against a System Test and three widely accepted system archetypes, confirming its fidelity. The paper highlights the need for a complete and widely accepted definition of systems thinking to enhance its educational and practical applications. The proposed definition includes elements such as recognizing interconnections, understanding feedback loops, differentiating types of stocks and flows, and modeling systems conceptually. This definition aims to provide a robust framework for teaching and applying systems thinking in various fields.