Short answers, pulled from the story.
A community is a social unit, a group of people, that shares a socially-significant characteristic such as place, norms, culture, religion, values, customs, or identity. Communities may share a sense of place in a geographical area like a country, village, town, or neighborhood, or in virtual space through communication platforms.
The English word community derives from the Old French comuneté, which in modern French is communauté. That word comes from the Latin communitas, meaning community and public spirit, which in turn comes from the Latin communis, meaning common.
In ecology, a community is an assemblage of populations, potentially of different species, interacting with one another. Ecologists distinguish major communities, which are self-sustaining and self-regulating like a forest or a lake, from minor communities, which rely on others, such as fungi decomposing a log.
In a 1986 study, McMillan and Chavis identified four elements of a sense of community: membership, a feeling of belonging; influence, the sense of mattering to a group; reinforcement, the integration and fulfillment of needs; and shared emotional connection. Chavis and colleagues later built a sense of community index, the SCI, from this work.
German sociologist Ferdinand Tönnies introduced the distinction in Gemeinschaft und Gesellschaft in 1887. Gemeinschaft, translated as community, stresses personal social interactions and the roles, values, and beliefs based on them, while Gesellschaft, translated as society or association, stresses indirect interactions, impersonal roles, and formal values. Tönnies held that no group is exclusively one or the other.
In The Different Drum, published in 1987, Scott Peck described four stages of conscious community building: pseudocommunity, where people present their friendliest characteristics; chaos, where they reveal their shadow selves; emptiness, where they acknowledge their own woundedness and brokenness; and true community, marked by deep respect and true listening. In 1991 he remarked that building a sense of community is easy but maintaining it is difficult.