The word norm coming from the latin word norma which means "angle measure" or (lawlike) "rule", has a number of meanings:

• A social or sociological norm; see norm (sociology).
• For philosophy, semantics and law, see norm (philosophy), which is a sentence or a meaning unit.
• A statistical concept in psychometrics.
• In mathematics, a norm can be
  • A map which assigns a length to vectors, see normed vector space. See also matrix norm.
  • The nonnegative integer function in the definition of Euclidean domain;
  • The product of conjugate elements of an algebraic element;
  • The field norm in algebraic number theory and Galois theory.
  • The reduced norm in the theory of algebras.
• Norm is also a character in the sitcom Cheers, and a spin-off, Norm.
• If you are looking for behavior norms on Wikipedia, try Wikipedia:wikiquette or http://c2.com/cgi/wiki?WikiSocialNorms

See related meanings in normal.