Which terms are best to use? Those from the scientific and technical communities prefer to use additive manufacturing when referring to the group of processes that build parts layer upon layer. An important reason is that it is the official standard term according to the ASTM F42 and ISO TC261 committees.
3D printing is, by far, most popular term. Google displays 20-30 times more references for 3D printing (or 3-D printing) compared to additive manufacturing. Today, many individuals and organizations use 3D printing and additive manufacturing interchangably.
Rapid prototyping was the most popular term years ago when prototyping dominated the use of the technology. Today, 3D printing is used for a wide range of applications including design and concept modeling, fit and function testing, patterns for casting, and mold and die tooling. It is also used for fixture and assembly tools, custom and replacement part manufacturing, short-run production, and series production. Prototyping remains an important application of the technology, but it is only one of many.