Solid Disc: one solid metal rotor
Vented Disc: two metal rotors joined together with separations in between
Cross Drilled Disc : one or two rotors with a pattern of holes drilled further improving cooling. also known as slotted rotor
here in pakistan most of us confuse cross drilled discs as ventilated. whereas solid discs without holes are also ventilated as described above. presently local corolla,civic all have vented discs (NOT CROSS DRILLED)