One important purpose of a definition is to explain the meaning of a word. Any problems associated with a definition may impede students' learning. However, research studies on the definitional problems from the perspective of physics education are limited. Physics educators may not be aware of the nature and extent of definitional problems. As an example, The Feynman Lectures of Physics suggest that there are at least four problems of definition: precision, circularity, context and completeness in knowledge. Feynman had the tendency of mentioning the words 'define' and 'definition' and discussing the problems of definition: they can be insightful, or challenge the conventional, preconceived notions of many physical concepts. One benefit of this study is that a framework can be developed to improve statements of definitions. This framework may guide educators or students to analyze the knowledge that is embedded in a definition. In the future, the learning of definition need not be content-oriented, but problem-based instead, with the help of definitional problems. Therefore, the use of these problems of definition in lessons can be an interesting area for future physics education research. Furthermore, we should be cognizant of inadequacies or inaccuracies in definition that may result in alternative conceptions.