3D is a term used for describing software that can create 3-dimensional imagery in animations that has now become very popular especially with blockbuster movies such as Toy Story, Jurassic Park, Lord of the Rings, Finding Nemo, Spiderman and many others. 3D is also used to describe the effect you see in the IMAX screens made popular with the movie Avatar.
3D content is also used in the video game industry such as Xbox, PlayStation, and Nintendo consoles to name a few. Architectural companies use the term 3D to describe 3D visualizations and fly-throughs of client homes.
3D content is created with a computer and software such as 3ds Max, Maya, Revit, and AutoCAD. The final animations (movie files) can be transferred from the computer to other mediums such as film, videotape, CD's, DVD's, and can also be published on the internet. The still images can be printed for magazines and physical models can be produced using a 3D printer.