The FASB has defined research and development cost in the following way:

reseach; planned search or critical investigation aimed at the discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, or in bringing about a significant improvement to an existing product or service.

development; the translation of research findings or other knowledge into a plan or design for a new product or service, or for a significant improvement to an existing product or service.

Thus, based on previous definitions, the following are examples of R&D activities:

Laboratory research aimed at discovery of new knowledge
Searching for applications of new research findings
Nonroutine modification of a product or process design
Design, construction, and testing of prototypes and models
Design of tools, jigs, molds, and dies involving new technology
design, construction, and operation of a pilot plant
engineering activity required to advance the design of a product to the manufacturing stage