There are many concepts in social sciences that are normative and controversial, and defined in different ways. Considering the principle of diverse understanding and constant dispute, it is impossible to reach to a final definition of these concepts so to be acceptable for all. At the condition of confusion and variety of interpretations in social sciences especially in political science, the contemporary British philosopher, Walter Bryce Gallie, proposed the idea of "Essentially Contested Concepts" in 1956 using the method of post-analytic philosophy. This idea seems to be a good step to reach a rational solution in understanding the important normative concepts that are constantly contested. In the first part of the paper, it is attempted to discuss Gallie’s idea and explain his criteria to accept a concept as "Essentially Contested", also different standpoints and critics over the idea are reviewed. In the second part, democracy as a key concept in political thought is selected and discussed, so to clarify whether or not democracy is an "Essentially Contested Concept". Finally, in a conclusion the importance and efficiency of Gallie’s idea in the contemporary world is emphasized and admired as a positive solution for a safe competition and a step toward pluralism and tolerance with other viewpoints.