“convention”

From a higher position to a lower one; downwards.

Something that provides a definitive characterization or description of the nature and attributes of a specified entity.

Distinguished by a unique, particular, or unusual quality.

A final examination; a test or examination given at the end of a term or class; the test that concludes a class.

A well-known convention (often the most well-known of a certain field) which supposedly can not or should not be broken.