This study attempts to understand the concept of the "deep state" given its increasing use in political literature and analysis. This happens especially in comparative studies and, specifically, when multiple political systems are addressed. Through an analysis of the literature in which the term is used, it is clear that the concept of the "deep state" is ambiguously understood and applied. This study is based on a critical view of the concept. It assumes that the vagueness of its definition is tinged with secrecy. Its fragmented usage in a variety of political systems (democratic, semi-democratic and authoritarian), render it an analytical tool that is not useful nor capable to expand knowledge of comparative political science. In lieu of this hypothesis, the study reveals discrepancies in the usage of the concept of "deep state", in an attempt to refine the concept.