An institution is an established custom or practice, or a group of people that was formed for a specific reason or a building that houses the group of people. (noun)
Marriage is an example of a cultural institution.
A town council is an example of an institution of government.
A place where those who are mentally ill go for treatment is an example of an institution.
A school where people go to learn is an example of an educational institution.
See institution in Webster's New World College Dictionary
noun
an instituting or being instituted; establishment
an established law, custom, practice, system, etc.
an organization, society, or corporation, having a public character, as a school, church, bank, hospital, etc.
the building housing such an organization
a person or thing long established in a place
See institution in American Heritage Dictionary 4
(ĭnˌstĭ-to͞oˈshən, -tyo͞oˈ-)
noun
The act of instituting.
a. A custom, practice, relationship, or behavioral pattern of importance in the life of a community or society: the institutions of marriage and the family.
b. Informal One long associated with a specified place, position, or function.
a. An established organization or foundation, especially one dedicated to education, public service, or culture.
b. The building or buildings housing such an organization.
c. A place for the care of persons who are destitute, disabled, or mentally ill.