A health indicator is a characteristic of an individual, population, or environment which is subject to measurement (directly or indirectly) and can be used to describe one or more aspects of the health of an individual or population (quality, quantity and time).
Reference: modified definition
Health indicators can be used to define public health problems at a particular point in time, to indicate change over time in the level of the health of a population or individual, to define differences in the health of populations, and to assess the extent to which the objectives of a programme are being reached.
Health indicators may include measurements of illness or disease which are more commonly used to measure health outcomes, or positive aspects of health (such as quality of life, life skills, or health expectancy), and of behaviours and actions by individuals which are related to health. They may also include indicators which measure the social and economic conditions and the physical environment as it relates to health, measures of health literacy and healthy public policy. This latter group of indicators may be used to measure intermediate health outcomes, and health promotion outcomes.