IS : Image stabilization is a family of techniques to increase the stability of an image. It is used in image-stabilized binoculars, photography, videography, and astronomical telescopes. With still cameras, camera shake is particularly problematic at slow shutter speeds or with long focal length (telephoto) lenses.

I've recently purhcased a canon 300mm with IS. This is a relatively newer technology that newer photographers aren't fully aware of its importance. YOU want a LENS with IS. If you can afford this technology in your lens, get it. It allows you too shoot at about 3 shutter speed settings longer with the same clarity. This is an INCREDIBLE advantage, especially for people that like to shoot indoors and dont have all this fancy expensive lighting crap.

-- I'm no pro at this stuff; for those of you that have seen my pictures on here-- That's pretty much the extent of my knowledge right there, but i'm learning-- and this is what I have learned. If anyone has more to add or think that some of this is BS, hit it up, this is an important topic for photographers

Yep. And in the Nikon-world it is called <!--coloro:red-->[color=red]<!--/coloro-->VR<!--colorc-->[/color]<!--/colorc--> (Vibration Reduction).