R&D stands for research and development and it is all about innovation. In Europe, the term is often expressed as RTD, standing for research and technical development.
It is about researching and developing the new technologies that will shape the market and the future.
Usually, medium to big corporations will have a R&D department of their own to carry out internal research projects. For example, Apple is one of those sort of companies.
Research and development activities are, however, not exclusive to technology companies, they are also used in other industries like pharmaceuticals.