The World Health Organisation defines health as “a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity”. 

The World Health Organisation defines a health system as “all the activities whose primary purpose is to promote, restore or maintain health”. The functions of a health system has been defined in a more detailed way by Maureen Mackintosh and Meri Koivusalo. At the core are health services, but these are complemented by public health functions (surveillance, prevention, cross-sectoral action and emergency preparedness); systems for training the people needed to staff the system (medical and nursing schools etc); and policy, ethical and regulatory decision-making bodies which direct the health systems and the people in them. 

Aid which is concerned with or seeking to promote human welfare.