A monk is a person who practices religious asceticism by monastic living, either alone or with any number of other monks.
In Theravada Buddhism, bhikkhu is the term for a monk. Their disciplinary code is called the patimokkha, which is a part of the larger Vinaya. They live lives of mendicancy, and go on a morning almsround every day. The local people give food for the monks to eat, though the monks are not permitted to ask for anything. The Theravada monks live in monasteries, and have an important function in traditional South-East Asian society. Bhikkhus do not eat dinner. The Latukikopama Sutta explains that the Buddha forbade monastics from going on alms rounds after noon to avoid dangers that they might meet later in the day—stumbling into natural dangers in the dark, being propositioned for a tryst in the twilight hours, random hooligans—and to prevent inconveniencing or frightening lay people.
Sugar, honey, and medicine are allowed in the afternoon according to all the different lineage. Due to the ingredients of pure dark chocolate being cocoa (a medicine) and sugar, monks in the Thai Forest tradition munch on the little dark squares at tea time.
Theravadan Monks are not supposed to lead a luxurious life. The Bhikkhus are only allowed 4 items (other than their robes): a razor, a needle, an alms bowl and a water strainer.
In Thailand and Burma, it is common for boys to spend some time living as a monk in a monastery. Most stay for only a few years and then leave, but a number continue on in the ascetic life for the rest of their lives.
Their rules forbid the use of money, although this rule is nowadays not kept by all monks. The monks are part of the Sangha, the third of the Triple Gem of Buddha, Dhamma, Sangha.
In Mahayana Buddhism, the term 'Sangha' strictly speaking refers to those who have achieved certain levels of understanding of the nature of emptiness. Several Mahayana orders accept female practitioners as monks, instead of using the normal title of "nun", and they are considered equal to male ascetics in all respects.
The Chinese Buddhist monks (who are part of the Mahayana Buddhism) practice the burning marks on their scalp, finger or part of the skin on their anterior side of the forearm with incense as a sign of ordination.
In Vajrayana Buddhism, monkhood is part of the system of 'vows of individual liberation'; these vows are taken in order to develop one's own personal ethical discipline. The monks and nuns form the Sangha. As for the Vajrayana vows of individual liberation, there are four steps: A lay person may take the 5 vows called 'approaching virtue'. The next step is to enter the monastic way of life which includes wearing monk's or nun's robes. After that, one can become a 'novice'. The last and final step is to take all vows of the 'fully ordained monk'.
Tibet's monasteries are also schools for monks.
The Tibetan word for monk is "trapa," which means “student” or “scholar." It is used to describe the three main categories of monastery residents: students (monks), and scholars and teachers (lamas). Monks and lamas don't necessarily have to be celibate. The religious leaders of many villages are married lamas.
Tibetan monks play a major role in the lives of the Tibetan people, conducting religious ceremonies and taking care of the monasteries.