Health is the functional and metabolic efficiency of an organism. It is the ability to live long, function well (physically and mentally), and prosper.

This collection of lists of health topics collects the names of topics related to health (including medicine).

In biology, an organism is any living system (such as animal, plant, fungus, or micro-organism). In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homeostasis as a stable whole. An organism may either be unicellular (single-celled) or be composed of, as in humans, many billions of cells grouped into specialized tissues and organs. The term multicellular (many-celled) describes any organism made up of more than one cell.

The term “organism” (Greek ὀργανισμός – organismos, from Ancient Greek ὄργανον – organon “organ, instrument, tool”) first appeared in the English language in 1701 and took on its current definition by 1834 (Oxford English Dictionary).

Scientific classification in biology considers organisms synonymous with life on Earth. Based on cell type, organisms may be divided into the prokaryotic and eukaryotic groups. The prokaryotes represent two separate domains, the Bacteria and Archaea. Eukaryotic organisms, with a membrane-bounded cell nucleus, also contain organelles, namely mitochondria and (in plants) plastids, generally considered to be derived from endosymbiotic bacteria. Fungi, animals and plants are examples of species that are eukaryotes.

More recently a clade, Neomura, has been proposed, which groups together the Archaea and Eukarya. Neomura is thought to have evolved from Bacteria, more specifically from Actinobacteria.

At the of the creation of the World Health Organization (WHO), in 1948, Health was defined as being “a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity”.

This definition invited nations to expand the conceptual framework of their health systems beyond issues related to the physical condition of individuals and their diseases, and it motivated us to focus our attention on what we now call social determinants of health. Consequently, WHO challenged political, academic, community, and professional organizations devoted to improving or preserving health to make the scope of their work explicit, including their rationale for allocating resources. This opened the door for public accountability .

Only a handful of publications have focused specifically on the definition of health and its evolution in the first 6 decades. Some of them highlight its lack of operational value and the problem created by use of the word “complete.” Others declare the definition, which has not been modified since 1948, “simply a bad one.” .

In 1986, the WHO, in the Ottawa Charter for Health Promotion, said that health is “a resource for everyday life, not the objective of living. Health is a positive concept emphasizing social and personal resources, as well as physical capacities.” Classification systems such as the WHO Family of International Classifications (WHO-FIC), which is composed of the International Classification of Functioning, Disability, and Health (ICF) and the International Classification of Diseases (ICD) also define health.

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