Throughout the centuries, the concept of "element" has undergone a clear evolution from a strictly philosophical area to the scientific domain, although the conceptual progress has not always gone along with a terminological evolution. Some inconsistencies in the definition of element can be found in several precollege and university-level textbooks, which creates confusion about the concepts of "element" and of "simple substance" and raises a teaching problem. In this paper, a survey of the historical evolution of the idea of element is followed by the critical review of some definitions of element found in the scientific literature and in textbooks. We discuss a definition of element consistent with current scientific knowledge that overcomes the ambiguity between the concepts of element and simple substance at the level of instruction.