An intersection is where two surfaces cross over each other. This line of intersection is used by DeskArtes to cut away parts of the surfaces.
Both trimming and blending cut away part of the surface. This is recorded as an attribute of the surface that is indicated by the line "->TRIM" in the Object Window below the surface. Clicking on this will cause the trim curves to be displayed. If a surface is trimmed with a second surface, the trim curves will be automatically combined by DeskArtes.