Convention

The act of coming together; the state of being together; union; coalition.

General agreement or concurrence; arbitrary custom; usage; conventionality.

A meeting or an assembly of persons, esp. of delegates or representatives, to accomplish some specific object, -- civil, social, political, or ecclesiastical.

An extraordinary assembly of the parkiament or estates of the realm, held without the king's writ, -- as the assembly which restored Charles II. to the throne, and that which declared the throne to be abdicated by James II.

An agreement or contract less formal than, or preliminary to, a treaty; an informal compact, as between commanders of armies in respect to suspension of hostilities, or between states; also, a formal agreement between governments or sovereign powers; as, a postal convention between two governments.

something regarded as a normative example; "the convention of not naming the main character"; "violence is the rule not the exception"; "his formula for impressing visitors"

(diplomacy) an international agreement

orthodoxy as a consequence of being conventional