A lightweight slab including two main parallel reticular reinforcements (5)(6) separated by secondary reinforcements and arranged to form a double diagonal, a single diagonal or to be perpendicular in relation to the main reinforcements. All of the reinforcements are embedded in a volume of concrete filling which covers and protects such reinforcements and which is defined by a suitable formwork or mould which creates voids in a hypothetical prismatic volume and which is formed by hollow prismatic or truncated-pyramid-shaped volumes with smooth edges and vertices that improve structural strength and facilitate the extraction of the moulds. The filling includes open holes (4, 3) in those portions that do not interfere with the secondary and main reinforcements to form a succession of nodes connected at the top and bottom by holes that can be accessed from the lower and/or upper level (4) and, internally, hollows (2) connected by side holes (3).