Latin: “from the earlier”.
In Epistemology the adjective used to describe beliefs, knowledge or other cognitive states that do not require previous experience.
For example, the proposition "All bachelors are unmarried men" can be known to be true in virtue of the definition of 'bachelor'. Or, the proposition, “Bachelors are bachelors,” is logically true because the predicate merely repeats the subject. All tautological, definitional, and analytical propositions (e.g., mathematical propositions) are described as a priori.
Rationalists (such as Rene Descartes and Plato) maintain that each mind (or soul) contains a set of beliefs which are independent of sensory experience. These “innate” ideas are usually thought to serve as a kind of epistemic foundation for the rest of our knowledge (see Internalism and Foundationalism).
Empiricists (such as John Locke and David Hume), on the other hand, tend to think of a priori ideas as abstractions from a posteriori ideas. What Locke calls “simple” ideas, or Hume labels “impressions” are the a posteriori atomic building blocks out of which compound/complex (a priori) ideas are built.
NOTE: the terms ‘innate’ and 'a priori’ are not synonymous. The former describes ideas that the mind/soul is thought to contain at birth, as opposed to ideas that are acquired through the course of one’s life. The latter is a description of the idea’s relationship to the process of experience. All innate ideas are a priori (if indeed there are any innate ideas), but not all a priori ideas are innate.