2-D means the front surface of your design will have two levels. One level is recessed, and the other is raised. Each level will be the same depth or height across the surface of the design. 3-D artwork also known as multi level artwork or a sculpted look. If an image has more than one height from the recessed level of the design surface, then it is considered 3-D.  3-D artwork can be created for your review prior to the production stage. The art below with the three dogs is a great example 2-d art versus 3-d art.