A bhikkhu (in Pāli, bhikṣu) is an ordained male Buddhist monk. The female monastic is called a bhikkhuni (in Pāli,bhikṣuṇī).
The Anagarika Dharmapala provided this description of bhikkus:
A Bhikku is one who aspires to follow the higher teachings of the Buddha and will take the ten vows. He may enter the monastic order if he has the consent of his parents and, in the case of a soldier, of his commander, and if he is free from contagious diseases. The ten vows are: not to kill; not to steal; to abstain from inchastity; to speak the truth; to abstain from intoxicating drinks and drugs; not to eat at forbidden hours (the bhikkhus are not supposed to partake of solid food after the midday meal); to abstain from dancing , music, theaters and all worldly amusement; not to use ornaments, perfumes and ointments; not to use luxurious beds; not to accept money. There are certain additional regulations in regard to discipline clothing and food, but otherwise the bhikku is free to reach his spiritual goal by any route, so long as he practices with faithfulness abstinence and self-denial...
I was fortunate in knowing well the Venerable H. Sri Sumangala, that most learned and beloved of bhikkhus, who until his death, in 1911, was the high priest of the Sri-pada, the Temple of the Sacred Footprint of the Buddha on Adam's Peak, where devout Buddhists have made pilgrimages for centuries."
- Anagarika Dharmapala, "On the Eightfold Path: Memories of an Interpreter of Buddhism to the Present-Day World," Asia (September, 1927), 721-722.