An ordained male Buddhist monk. Female versions are called Bhikkhunis.
1. "And what, bhikkhus, is that middle way awakened to by the Tathagata, which gives rise to vision ... which leads to Nibbana? It is this noble eightfold path; that is, right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, right concentration.
(Siddhartha Gautama from Turning the wheel of Dhamma)