Product development is the entire process of researching, designing, creating, testing, marketing, and selling new products. Research and development is essentially the first step in developing a new product, but product development is not exclusively research and development. It is the entire product life cycle, from conception to sale.
Product development is also not exclusive to designing, implementing, and selling new products. Existing products can go through product development to revamp old features or add new features so the product sells better or adds greater value to consumers. Any time a new product is created and sold—or any time an existing product has added features and is resold—it is going through product development.