Usual langage pratices of industrial maintenance are rather different from those used during the power plants design. Maintenance is part of O&M (Operation & Maintenance) whose concepts are more “operational” than the ones of design phases. As co-researches in this work, we instigated these practices for a better understandability between semantic fields, as this inquiry offers food for thought, the theoretical as well as the practical. Also, the role of ontologies are questioned while the real case study are from the EDF (Electricity of France) power plants.