Additive Manufacturing
Additive manufacturing is a relatively new manufacturing method which has become a key area of interest in multiple industrial sectors. Based on CAD models the process enables creating solid, yet highly complex, parts and push towards a tool-less manufacturing environment, with both improved quality and better efficiency in many cases.

Additive manufacturing (AM) is the process of joining materials to make objects from Computer-Aided Design (CAD) model data, as opposed to subtractive manufacturing methods where material is removed. Additive manufacturing is often a layer by layer process and is also called 3D printing, additive fabrication, or freeform fabrication.
Composites Manufacturing — Layer by layer

If you look at the composites industry, one can claim that creating a composite laminate is the original additive manufacturing process. The idea behind additive manufacturing is that you build up a structure layer by layer to form the complete part, rather than the traditional subtractive process of taking a block of something and removing material.
I have personally built composites structures; cutting the plies and laying them down layer by layer on shaped molds to make dish antennas or solar panels. The key thing you would notice is the pre-cut sheets are laid manually whereas in the AM the process, a machine lays down strips of material with very little human input.
Comparison of AM and Composites Manufacturing
One of the greatest benefits of AM is the low amount of pre- and post-processing required to get the finished part. AM starts with a blank canvas and, depending on the complexity, creates products without the need for finishing processes. This also means the amount of waste material is kept to a minimum. Composites manufacturing on the other hand requires a pre-made form for layup and is followed by some kind of curing and finishing steps. This makes AM very cost effective.