The source of article:
http://degreedirectory.org/articles/What_is_the_Difference_Between_CAD_and_AutoCAD.html
Types of CAD Depending on the type of work you will need to perform, there are different forms of CAD that you may employ. 2-dimensional, 2.5-dimensional and 3-dimensional models each present different types of images in different perspectives.
2-dimensional drafts are flat, while 3-dimensional and 2.5-dimensional drawings are useful if you'd like to examine the depth and space of a design.
I can understand 2 and 3 dimensional CAD, but have no idea what is 2.5 dimension:?
Also if you know any Autodesk product in this field, let me know.