Sigma lens for a Nikon?

I'm looking to buy an 18-200mm lens for my Nikon D3100. I've found one from "Sigma" which is an "Optical Stabilizer Lens for Nikon." What does "Optical Stabilizer" mean, and is this a good brand? Will my pictures be good quality?

Sigma's Optical Stabilizer is their equivalent of Nikon's Vibration Reduction - different names for the same thing.

You'll want the HSM version, though - Sigma's equivalent of Nikon's AF-S - built-in focus motor.

Opinion is divided, some Sigma lenses are nice, some not as good. Their best aren't quite as good as Nikkors but they're cheaper. You'll probably notice the difference in price more than in performance.

The brand is Sigma. It's not as good as Nikon so the price shows it.

http://keerok-photography.blogspot.com/2011/05/third-party-lenses.html

Sigma's Optical Stabilizer (OS) is equal to Nikon's Vibration Reduction (VR).It's an anti-shake feature to make pictures sharper.