A branch of science for understanding humans and their interaction with technology and the environment. 

Concerned about the human function in the design,  known as an interdisciplinary of psychology, human capability, and human-computer interaction.

How to apply what we know about humans — such as cognitive, and physical abilities and limitations — as multiple aspects in the core design.

Human factors psychology can be applied to almost all everyday design. It is a tool to solve challenges and to create new possibilities.  The role of human factor research is to innovate and to enhance a current experience, a product or service, in order to make it more usable, safer, or pleasant to use.