V-Power spark plugs are a patented design by NGK to improve ignitability and reduce quenching. Ignitability is improved by the V-groove cut in the center electrode parallel to the ground electrode, this directs the spark to to the edge of the center electrode thus exposing it to more of the air/fuel mixture. Quenching
is reduced in much the same manner, drawing the spark to the edge of
the center and ground electrodes reduces the surface area available to
quench the spark. See quenching for more info.