Ergonomics, also called comfort design or functional design, is the practice of designing products, systems, and processes taking into consideration their interaction with the ones that use them and, more generally, with people.
Many disciplines participate in Ergonomics: psychology, engineering, industrial design etc.
Hereby is the definition of Ergonomics from The International Ergonomics Association:
Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance.