A bhikkhu (monk) is a man who has renounced ordinary society to live a celibate monastic life.
Monks are expected to have eight simple requisites and to live by the 227 rules of the Vinaya. Someone can become a novice (samanera) while still a boy but must be twenty years old or over to be a fully ordained monk (upasampadà). If he loses interest in the monastic life, a monk can leave at any time. The most characteristic features of Buddhists monks are their yellow robes, their shaven heads and their calm, smiling demeanour.