Definition of Ergonomics and
Human Factors:
Ergonomics and Human Factors is the systematic application of relevant information about human capabilities, limitations, characteristics, behavior and motivation to the design of machines, tools, procedures, and processes used by people and the environment in which they use them.
Ergonomists tend to focus on physical, or "neck-down", issues with an emphasis on understanding the role of human movement and posture as it relates to work.
Human Factors Professionals (primarily those with psychology and engineering backgrounds) tend to focus on cognitive, or "neck-up", ergonomics with an emphasis on information processing issues related to work.