Definition of institution:
an organization founded and united for a specific purpose
an establishment consisting of a building or complex of buildings where an organization for the promotion of some cause is situated
a custom that for a long time has been an important feature of some group or society; "the institution of marriage"; "the institution of slavery"; "he had become an institution in the theater"
the act of starting something for the first time; introducing something new; "she looked forward to her initiation as an adult"; "the foundation of a new scientific society"
a hospital for mentally incompetent or unbalanced person