Benefit sharing has been a recurrent theme in international debates for the past two decades. However, despite its prominence in law, medical ethics and political philosophy, the concept has never been satisfactorily defined. In this conceptual paper, a definition that combines current legal guidelines with input from ethics debates is developed. Philosophers like boxes; protective casings into which they can put concisely-defined concepts. Autonomy is the human capacity for self-determination; beneficence denotes the virtue of good deeds, coercion is the intentional threat of harm and so on. What about benefit sharing? Does the concept have a box and are the contents clearly defined? The answer to this question has to be no. The concept of benefit sharing is almost unique in that various disciplines use it regularly without precise definitions. In this article, a definition for benefit sharing is provided, to eliminate unnecessary ambiguity.