Few handgunners really know where the term "Magna" grips comes from, and how they differ from any other grip.
On Smith & Wesson revolvers, Magna grips are wooden grips that extend upward to the top of the frame. They do not include the filler block behind the trigger guard, which is often hard for small hands to manage.
Magnas were contrived to prevent the sharp edge at the rear of the frame from digging into the shooter's hand. They were the standard issue on many guns (Model 58s, 28s and others) for decades.
Legend holds that they came from a little guy with a great big hat who came from out Idaho way.