1.NounThe branch of philosophy dealing with the study of knowledge; the theory of knowledge, asking such questions as "What is knowledge?", "How is knowledge acquired?", "What do people know?", "How do we know what we know?", "How do we know it is true?", and so on.
"Some thinkers take the view that, beginning with the work of Descartes, epistemology began to replace metaphysics as the most important area of philosophy."
2.NounA particular instance, version, or school thereof; a particular theory of knowledge.
"In his epistemology, Plato maintains that our knowledge of universal concepts is a kind of recollection."