This International Standard defines terms in the field of mental work-load, covering mental stress and mental strain, short and long term, positive and negative consequences of mental strain. This International Standard specifies the relations between these concepts involved. Mental work-load in this International Standard is regarded as an umbrella or generic term, referring to all the concepts and constructs mentioned in this International Standard and does not have a specified or standardized meaning of its own within this International Standard. This is consistent with the use of the term in ergonomics and its applications, where it can refer to mental stress, mental strain and their effects, i.e. both to the causes and the effects. In this International Standard the term mental work-load will not be treated as a technical term but only as a reference to the domain of mental work-load. This International Standard applies to the design of working conditions with respect to mental work-load and is intended to promote a common usage of terminology between experts and practitioners in the field of ergonomics as well as in general. This International Standard does not address methods of measurement and principles of task design, which are dealt with in ISO 10075 2 and ISO 10075 3.