In January 2007 the World Nuclear Association (WNA) established the Cooperation in Reactor Design Evaluation and Licensing Working Group (CORDEL) with the aim of stimulating a dialogue between the nuclear industry and nuclear regulators on the benefits and means of achieving a worldwide convergence of safety standards for reactor designs. CORDEL is comprised of several technical working groups including the Digital Instrumentation and Control Task Force (DICTF). Soon after CORDEL was established, the DICTF identified safety classification as a topic where a better understanding of the regulatory practices in various countries could improve the nuclear industries’ ability to license new nuclear power plant designs in various countries. One of the issues identified was the need to understand inconsistencies between the safety requirements established by international and national codes and standards. The first step in this effort was to examine the formally defined terminology that the various organizations use to define five key concepts: Defense-in-depth and diversity, Separation, Redundancy, Reliability, and Spurious activation. This paper summarizes the approach and conclusions of this study. We found important inconsistencies both between the terms that various organizations use for the above key concepts and the definitions of the key concepts themselves. We also found, however, that some of the existing definitions encompass the ideas of all of the organizations studied. Therefore, we believe that it is possible to establish common terms and definitions for the five concepts. This work may also represent a prototype methodology for harmonizing terms and definitions used for other key concepts.