Institution and its definition

Institution.
I am having difficulty finding an institution. What is an institution? Family? Catholicism? McDonalds?..."political", "religious", "art" institutions... What are the boundaries between those? I am more interested in the idea of an informal institution created by
"informal social order and organization, reflecting human psychology, culture, habits and customs" and institutions "arise, develop and function in a pattern of social self-organization, which goes beyond the conscious intentions of the individual humans involved".

Wikipedia goes on to give examples of institutions such as Open Source. In this sense, Facebook could be considered as an institution. The city as an institution? Underground commuters as another institution in which set of customs are prescribed by that environment; reading, sitting, standing, tin music from earphones...


This the Wikipedia definition of institution, http://en.wikipedia.org/wiki/Institution,

Institutions are structures and mechanisms of social order and cooperation governing the behavior of a set of individuals. Institutions are identified with a social purpose and permanence, transcending individual human lives and intentions, and with the making and enforcing of rules governing cooperative human behavior. The term, institution, is commonly applied to customs and behavior patterns important to a society, as well as to particular formal organizations of government and public service. As structures and mechanisms of social order among humans, institutions are one of the principal objects of study in the social sciences, including sociology, political science and economics. Institutions are a central concern for law, the formal regime for political rule-making and enforcement. The creation and evolution of institutions is a primary topic for history.