RD is actually "R&D" which means research and development. It is exactly what it means, a chef, usually working for a corporation that works on developing new products. They watch the trends to see what the next fad is, they create new menu items and then figure out how to implement them, no small task when you are the McDonald's R&D chef. In the world of supermarket foods this position can be more of a chemist's job as they seek ways to create shelf-stable foods. In fact there is a trend among some schools to offer a "food chemistry" degree that combines cooking and chemistry.