The environmental assessment is supported by several concepts which determine the instruments to be applied or the conduct to be followed according to the missions assigned to the stakeholders. In the projects, the various actors, even those in charge of environmental and social monitoring, have several gaps in their knowledge. This results in ineffectiveness in the implementation of environmental management for ongoing projects. Hence the author's idea of designing a lexicon of environmental and social assessment. This tool brings together all the useful terms and concepts, on the one hand during the development of safeguard instruments and, on the other hand, during environmental and social monitoring. This tool is the palliative to the shortcomings of those involved in environmental and social assessment. For more efficiency, the lexicon was digitized in a computer application having the capacity to facilitate the research of the concepts as well to know their use as for their meaning. Via this lexicon, definitions and explanations of concepts related to environmental and social assessment in general and environmental monitoring in particular, are accessible to all stakeholders.