Work at Xerox PARC, Apple, Loughborough University, Carnegie-Mellon University and the University of California at San Diego considered how people worked with existing computer systems and how to make that interaction more efficient and easier. The bulk of early HCI designers and especially evaluators were cognitive psychologists. These trends lead to an enormous number of different methods in regular use for the evaluation of usability. We might see three main kinds of usability evaluation - expert, empirical and contextual. These formal methods will not be considered any further here.
Heuristic evaluation has more usefulness to it.
It relates to the evaluation of the system by its designers according to their own intuitive understandings of quality, published guidelines for good design such as the Apple Human Interface Guidelines, or checklists of broad signs of usability. The two keys points about this is that it is what most designers do anyway and that it's easy. This is typically part of a formative evaluation to redesign the interface, or the whole application, based on users' responses, experiences and problems. These methods tend to derive from cognitive and social psychology, but the defining characteristic is their place of study, being the laboratory rather than the workplace. There are many methods in use in laboratory studies of usability.