For an individual, a "social obligation" is an informal need to do something based on prescribed social etiquette. Reciprocating an invitation to dinner is a social obligation when a person doesn't really want to do it. For businesses, a social obligation is an informal need to give back to society.
Social obligations are established over time based on social norms. Someone may attend a neighborhood block party even though the person isn't friendly with many of the people in the neighborhood. Some of the ways in which companies meet social obligations include donating to local charities, participating in community events and being transparent with the public.