When creating a mesh interface between 2 zones, Fluent will look at what are the overlapping and non-overlapping sections between the different sides of the interface. If the interface connects different fluid zones, the following boundary zones will be created : -Interface Interior Zone : this corresponds to the overlapping section through which will go the fluid flow -Boundary Zone 1 and Boundary Zone 2 : those correspond to the non-overlapping sections for each of the connected zones If the interface connects different solid zones (Coupled Wall), the following boundary zones will be created : -Interface Wall Zone 1 and Interface Wall Zone 2 : this corresponds to the overlapping section, through which will occur the heat transfer, split into a wall and a wall shadow, for each of the connected zones. -Boundary Zone 1 and Boundary Zone 2 : those correspond to the non-overlapping sections for each of the connected zones For additional information, the interface creation procedure for non-conformal meshes is fully described in the section “Non-Conformal Meshes” of Fluent User Guide.