Scholars have long debated the definition of social entrepreneurship, but disagreement persists. Despite sustained efforts to craft a universal definition, social entrepreneurship has been characterized as an ʻessentially contested concept’. However, little is known about the root causes of this ongoing contestation. Therefore, we delve into the literature's social entrepreneurship definitions to examine this complex issue. Our systematic literature review leverages insights from the philosophy of science and formal logic—specifically, a theory of definition—to present four rules for definitional evaluation in the social sciences. Accordingly, definitions should convey the essence of a concept (Rule 1: essence), differentiate between their defining and defined terms (Rule 2: expression), be phrased positively (Rule 3: explication), and avoid figurative and obscure language (Rule 4: eloquence). Using these rules to analyse 156 original social entrepreneurship definitions reveals varying interpretations of the concept's essence and sheds light on epistemological issues, such as tautological definitions. Integrating these findings into a practical ʻrulebook’ for definitional evaluation significantly contributes to the social entrepreneurship literature and other highly contested fields by helping to understand different sources of contestation. Guided by our rulebook, we suggest future research avenues and highlight diverse theorizing styles, the engagement of opposing and paradoxical definitional views and the role of academic language in shaping the social entrepreneurship field.