"Hermit" is a term used to describe people who live away from groups of people and do not engage with other people very much socially. The term does have some religious connotations but has passed into regular use without a religious definition. The term can be applied to outcasts as easily as people who choose social isolation. It can apply to people with depression, scant social skills, or even just an isolated homestead.
The origins of the term hermit lie with Christian religions. Hermits were people who went away from society to connect with their god, to pray or to ponder a specific problem. These people were gone for quite a long time—traditionally 40 years. Other religions, such as Buddhism and Taoism, have a tradition of social isolation among the devout.
Several mental illnesses, particularly anxiety disorders and depression, can lead to a condition called agoraphobia. This term translates literally as "fear of the marketplace." A phobia is a fear and agora is the ancient Greek term for the marketplace or central meeting place in the town. This fear leads agoraphobics to avoid social situations and places where there are a lot of people. It is common for these people to become hermits that spend most of their time at home or within a comfortable range from home.
Sometimes people become hermits because of other people and not because of a choice they made. Some societies will shun members of the society, harass them or even formally force them to live apart through some archaic law. Because these people live apart from the group and do not socialize as much as their peers do, they are hermits, even though they are sometimes unwilling.
Illness can drive some people away from society. This is usually because the hermit is ill and the rest of the society does not want to catch the illness, not the other way around. This is seen particularly often, and still at the time of publication, among lepers. Towns will often send their lepers to live in communities with each other, but lepers may live alone away from society as well.
Vocational or intellectual endeavors
Adventurous types, some biologists, some researchers and the like, are forced to live away from society for long periods of time because the subject of their interest is far away from society. For example, a biologist studying an animal that lives in remote locations may spend decades away from society and living near the creature he or she is researching.
Some agricultural pursuits and other jobs require living on big stretches of land with little or no surrounding community. However, that is not the only economic reason a person might move to a secluded area. If a person has little money or wants to save money, land is cheaper in this secluded area, and if he or she can still earn a living that far from society, moving away and living a secluded life is a cheaper choice than staying.