Definition of "contravariance"

contravariance

noun
countable and uncountable, plural contravariances
1. (object-oriented programming) The reversal of the order of data types acted upon by an operator.
  Quotations
  I get why with covariance I can return a Dog (a Dog is a Mammal), but why does contravariance work the other way? Shouldn't it accept a derived type when it expects a base type? Contravariance is consistent with Postel's Law: […]
  2005, Jesse Liberty, Visual C# 2005: A Developer's Notebook, O'Reilly Media, page 47
2. (category theory) A functor which reverses composition.
3. (linear algebra) Of vectors, the property of scaling inversely with a change of basis, as opposed to covariance.