It's often applied to things involving inductive reasoning, which uses specific instances to arrive at a general principle or law (from effect to cause). It can be used as an adjective, as in a posteriori knowledge, or as an adverb, as in We acquire knowledge a posteriori—through experience.

What is an example of a posteriori?

A posteriori is a judgment or conclusion based on experience or by what others tell us about their experiences. For example, I know the Sun will set this evening because it always has. My a posteriori knowledge tells me that the sun will set again.

What does the term a posteriori mean?

A posteriori, Latin for "from the latter", is a term from logic, which usually refers to reasoning that works backward from an effect to its causes.