A need is something that is necessary for an organism to live a healthy life. Needs are distinguished from wants in that, in the case of a need, a deficiency causes a clear adverse outcome: a dysfunction or death. Basic needs such as water, air, food and protection from environmental dangers are necessary for an organism to live.
Needs can be objective and physical, such as the need for food, or psychological and subjective, such as the need for self-esteem.
There are also needs of a social or societal nature.
Needs and wants are a matter of interest in, and form a common substrate for, the fields of philosophy, biology, psychology, social science, economics and politics.