Social capital includes kin networks, group membership, socio-political voice and influence.
Social capital is a form of economic and cultural capital in which social networks are central, transactions are marked by reciprocity, trust, and cooperation, and market agents produce goods and services not mainly for themselves, but for a common good. The term generally refers to (a) resources, and the value of these resources, both tangible (public spaces, private property) and intangible ("actors", "human capital", people), (b) the relationships among these resources, and (c) the impact that these relationships have on the resources involved in each relationship, and on larger groups. It is generally seen as a form of capital that produces public goods for a common good. Social capital has been used to explain the improved performance of diverse groups, the growth of entrepreneurial firms, superior managerial performance, enhanced supply chain relations, the value derived from strategic alliances, and the evolution of communities. During the 1990s and 2000s the concept has become increasingly popular in a wide range of social science disciplines and also in politics.
Source: Wikipedia - Social capital