Ergonomics derives from two Greek words: ergon, meaning work, and nomoi, meaning natural laws. Combined they create a word that means the science of work and a persons relationship to that work.
In application ergonomics is a discipline focused on making products and tasks comfortable and efficient for the user.
Ergonomics is sometimes defined as the science of fitting the work to the user instead of forcing the user to fit the work. However this is more a primary ergonomic principle rather than a definition.