That which is normal or typical.
A rule that is enforced by members of a community.
A sentence with non-descriptive meaning, such as a command, permission or prohibition.
A function, generally denoted v\mapsto\left|v\right| or v\mapsto\left\|v\right\|, that maps vectors to non-negative scalars and has the following properties:
A high level of performance in a chess tournament, several of which are required for a player to receive a title.