3D modeling is when you create 3D and realistic looking images and videos. The results can be very mind blowing, with some hard to tell that it's not real. Below are a few links to get a general knowledge of what many use to create these amazing works.
ZBrush
3D modeling and texture program.
Maya, 3D Studio Max, and Mudbox
All of these are 3D modeling programs. Used for both creating 3D
animations and 3D image stills. Textures for models are created using
another program. A lot use Photoshop for this.
Mudbox
http://usa.autodesk.com/adsk/servlet/pc/index?id=13565063&siteID=123112
Mudbox
http://usa.autodesk.com/adsk/servlet/pc/index?id=13565063&siteID=123112
3D sculpting and texture program
V-Ray
Used as an extension to a modeling program. Works with the lighting effects, and makes high quality and realistic looking renders.
Mental Ray
Another rendering program
And to check out some images of what can be created with these programs check out this link: