The prescriptive definition of “emotion” has still kept absent even though the number of research into emotion increases steadily. To think whether the established definition of emotion was needed or not, we discussed possible problems caused by the lack of definition of emotion. First discussion focused problems about definition of emotion that emphasizes specific components of emotion. Then, complicated relationship between emotion and cognition was reviewed. This review showed the problems caused by inconsistent conceptualization and blurred boundary, and tried to illustrate ambiguity of the term emotion. Conceptual ambiguity might lead to vacuity of theoretical debate and research. In addition, we focused on the context-dependency of the emotion, and suggested that the context-dependent usage could impede conceptual development for proper description of behavior. Finally, we concluded that the lack of definition of emotion should limit the progress of the research in this domain at least potentially. To establish the prescriptive definition of emotion in the near future, paying more attention to the context information where the emotion exists, the cautious use of the term emotion was suggested.