What does a posteriori mean?
The definition of a posteriori
A` pos*te`ri*o”ri.
Etym: [L. a (ab) + posterior latter.]

1 (Logic)
Characterizing that kind of reasoning which derives propositions from the observation of facts, or by generalizations from facts arrives at principles and definitions, or infers causes from effects. This is the reverse of a priori reasoning.
2 (Philos.)
Applied to knowledge which is based upon or derived from facts through induction or experiment; inductive or empirical.