What is Institution?

Legal Definition
Institutions are "stable, valued, recurring patterns of behavior". As structures or mechanisms of social order, they govern the behaviour of a set of individuals within a given community. Institutions are identified with a social purpose, transcending individuals and intentions by mediating the rules that govern living behavior.

The term "institution" commonly applies to both informal institutions such as customs, or behavior patterns important to a society, and to particular formal institutions created by entities such as the government and public services. Primary or meta-institutions are institutions such as the family that are broad enough to encompass other institutions.

As structures and mechanisms of social order, institutions are a principal object of study in social sciences such as political science, anthropology, economics, and sociology (the latter described by Émile Durkheim as the "science of institutions, their genesis and their functioning"). Institutions are also a central concern for law, the formal mechanism for political rule-making and enforcement.
-- Wikipedia
Legal Definition
Eccl. law. The act by which the ordinary commits the cure of souls to a person presented to a benefice.
-- Bouviers Law Dictionary
Legal Definition
Political law. That which has been established and settled by law for the public good; as, the American institutions guaranty to the citizens all privileges and immunities essential to freedom.
-- Bouviers Law Dictionary
Legal Definition
Practice. The commencement of an action; as, A B has instituted a suit against C D, to recover damages for a trespass.
-- Bouviers Law Dictionary
Legal Definition
The commencement or inauguration of anything. The first establishment of a law, rule, rite, etc. Any custom, system, organization, etc., firmly established. An elementary rule or principle. In practice. The commencement of an action or prosecution; as, A. B. has instituted a suit against C. D. to recover damages for trespass. In political law. A law, rite, or ceremony enjoined by authority as a permanent rule of conduct or of government Webster. A system or body of usages, laws, or regulations, of extensive and recurring operation. containing within itself an organism by which it effects its own independent action, continuance, and generally its own further development. Its object is to generate, effect, regulate, or sanction a succession of acts, transactions, or productions of a peculiar kind or class. We are likewise in the habit of calling single laws or usages "institutions," if their operation is of vital importance and vast scope, and if their continuance is in a high degree independent of any interfering power. Lieb. Civli Lib. 300. In corporation law. An organization or foundation, for the exercise of some public purpose or function; as an asylum or a university. By the term "institution" in this sense is to be understood an establishment or organization which is permanent in its nature, as distinguished from an enterprise or undertaking which is transient and temporary. Humphries v. Little Sisters of the Poor, 29 Ohio St 206; Indianapolis v. Stur-devant, 24 Ind. 391. In ecclesiastical law. A kind of investiture of the spiritual part of the benefice, as induction is of the temporal; for by institution the care of the souls of the parish is committed to the charge of the clerk. Brown. In the civil law. The designation by a testator of a person to be his heir. In jurisprudence. The plural form of this word ("institutions") is sometimes used as the equivalent of "institutes," to denote an elementary text-book of the law.
-- Black's Law Dictionary
Legal Definition
Same as Induction. Also an establishment of a public character; a place where the business or a society is carried on; the organization itself. See 80 Ga. 159, 7 S. E. 633.
-- Ballentine's Law Dictionary