While one might envision a Nerf Bar to resemble the Nerf Football, it does not. It is actually a tubular step mounted on the side of a Pickup, Van, SUV, or the like, helping the driver and passenger get up into the vehicle.
Like so many cool things on our street and off road vehicles, these originated in auto racing. Seems like they are always the true pioneers in things related to functionality and safety! They attached these round bars to the sides of their race cars to allow them to "NERF" or bump slightly another car to move it out of the way, or to move around it. Without them, the NERF would've been done by the wheels, which would have had bad results. Picture cars flipping, going air born, and like that. Not good. So they came out with these bars for NERFING, and called them Nerf Bars.
The Nerf Bars looked cool, and it was an easy transition to use them for side steps. ( And, no, this doesn't mean you can use them to bump that car next to you on the interstate out of the way!! They're steps!! ) All part of the running board, side step family. The tubular steps are the ones referred to as Nerf Bars, although some have called them Tube Steps and Side Bars.
They are usually made out of some pretty tough and sturdy material, like steel, and come with a stainless, chrome, or black powder coat finish. They mount up under the doors / side panel and installation is fairly quick and easy thanks to their shape. They like to be matched up with bull bars or grille guards, and other such accessories. They make great off-road pieces and can help protect your vehicle from rocks and stumps along the trail!
Whether your travels are on the road or off, they really do a great job of helping you get up into the taller pickups, vans, and SUVs. Especially when it's icy or wet, as they give you an extra foot hold climbing in. I think they're easier to center your foot on than a traditional running board step. But that's just me. Whatever your reasoning or logic for wanting a nice set of nerf bars for your rig, you can find them all over the net at aftermarket auto accessories web stores. So grab your board, Dude, cuz Nerf's up!