Is there a difference between 3D printing and additive manufacturing?
Yes and No at the same time:
3D Printing is a subset of Additive Manufacturing
but treated as a synonym at this time
3D printing is a process that takes some material, in a fluid state that fuses with the model to shape an object from it. The material could be plastics, ceramic paste or even metal. The fluid state could be the normal state, or just be present for the fusing process (think powder and resin based systems), or be a transitional phase (as in filament based systems).
Additive manufacturing is just a slight bit bigger: at the moment most, if not all, AM processes are some sort of 3D printing. But AM could include other processes that don't fit 3D printing. For example, an automatic bricklaying machine could, under some view, be Additive Manufacturing, but it is not 3D printing in the traditional sense.
So: All 3D Printing is Additive Manufacturing, but not all Additive Manufacturing is necessarily 3D Printing.