Life is a condition that distinguishes organisms from inorganic objects, i.e. non-life, and dead organisms, being manifested by growth through metabolism, reproduction, and the power of adaptation to environment through changes originating internally. A physical characteristic of life is that it feeds on negative entropy.^[1][2] In more detail, according to physicists such as John Bernal, Erwin Schrödinger, Wigner, and John Avery, life is a member of the class of phenomena which are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form (see: entropy and life).^[3][4]

A diverse array of living organisms can be found in the biosphere on Earth. Properties common to these organisms—plants, animals, fungi, protists, archaea and bacteria—are a carbon- and water-based cellular form with complex organization and heritable genetic information. They undergo metabolism, possess a capacity to grow, respond to stimuli, reproduce and, through natural selection, adapt to their environment in successive generations.

An entity with the above properties is considered to be a living organism, that is an organism that is alive hence can be called a life form. However, not every definition of life considers all of these properties to be essential. For example, the capacity for descent with modification is often taken as the only essential property of life. This definition notably includes viruses, which do not qualify under narrower definitions as they are acellular and do not metabolise. Broader definitions of life may also include theoretical non-carbon-based life and other alternative biology. Some forms of artificial life, however, especially wet artificial life, might alternatively be classified as real life.

However, others cite several limitations of this definition^[7]. Thus, many members of several species do not reproduce, possibly because they belong to specialized sterile castes (such as ant workers), these are still considered forms of life. One could say that the property of life is inherited; hence, sterile or hybrid organisms such as the mule, liger or eunuchs are alive although they are not capable of self reproduction. However, (a) The species as a whole does reproduce, (b) There are no cases of species where 100% of the individuals reproduce as some are killed before they can, etc, and (c) specialized non-reproducing individuals of the species may still partially propagate their DNA or other master pattern through mechanisms such as kin selection.