Apikoros (perhaps from the Greek «Epicurean»), is a term designating a person who leaves the rabbinic tradition.
The term first occurs in the Midrash, and is defined by Maimonides as anyone who rejects revelation and prophecy, or who insists that God has no knowledge of human activity. Currently the term is used to describe anyone holding heretical or heterodox views. A.G.H.
Source:
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, p. 80