Human factors is a term that covers:

The science of understanding the properties of human capability (Human Factors Science).
The application of this understanding to the design and development of systems and services (Human Factors Engineering).
The art of ensuring successful application of Human Factors Engineering to a programme (sometimes referred to as Human Factors Integration).
The term "human factors science/research/technologies" is to a large extent synonymous with the term "ergonomics", having separate origins on either side of the Atlantic Ocean but covering the same technical areas.

In general, a human factor is a physical or cognitive property of an individual or social behavior which is specific to humans and influences functioning of technological systems as well as human-environment equilibriums.

The recognition and study of human factors is important for safety because they can be the cause of serious human errors on the levels of physical behavior and socio-cognitive decision-making ( A.M.Gadomski).

In social interactions, the use of the term human factor stresses the social properties unique to or characteristic of humans.

Human factors involves the study of all aspects of the way humans relate to the world around them, with the aim of improving operational performance, safety, through life costs and/or adoption through improvement in the experience of the end user.

The terms human factors and ergonomics have only been widely used in recent times; the field's origin is in the design and use of aircraft during World War II to improve aviation safety. It was in reference to the psychologists and physiologists working at that time and the work that they were doing that the terms "applied psychology" and “ergonomics” were first coined. Work by Elias Porter, Ph.D. and others within the RAND Corporation after WWII extended these concepts. "As the thinking progressed, a new concept developed - that it was possible to view an organization such as an air-defense, man-machine system as a single organism and that it was possible to study the behavior of such an organism. It was the climate for a breakthrough."