A monk ( , monachos), derived from Greek monos (alone), in modern parlance also referred to as a monastic, is a person who practices religious asceticism, the conditioning of mind and body in favor of the spirit, and does so living either alone or with any number of like-minded people, whilst always maintaining some degree of physical separation from those not sharing the same purpose. The concept is ancient and can be seen in many religions and in philosophy.

In the Greek language the term can apply to men or women; but in modern English it is in use only for men, while nun is used for female monastics.

Although the term monachos (“monk”) is of Christian origin, in the English language it tends to be used analogously or loosely also for ascetics from other religious or philosophical backgrounds.

The term monk is generic and in some religious or philosophical traditions it therefore may be considered interchangeable with other generic terms such as ascetic. However, being generic, it is not interchangeable with terms that denote particular kinds of monk, such as cenobite, hermit, anchorite, hesychast, solitary.

Etymology

Nowadays it is often wrongly assumed that it signifies a monk living in community, who is merely one kind of monk who lives with other monks, namely a cenobite (Greek: κοινοβιακός).

From early Church times there has been a lively discussion of the meaning of the term monk (derived from Greek: monos, alone), namely whether it denotes someone living alone/away from the rest of society, or someone celibate/focused on God alone. The Western rule giver Benedict of Nursia understood it as meaning the latter, namely a celibate dedicated to God. This is evident from the fact that his list of the four kinds of monks includes hermits.

The four kinds of monks identified by Benedict of Nursia in chapter 1 of his Rule for Monks as well as in the Rule of the Master are the following:

1. The cenobites live in community in a monastery, serve God under a religious rule and do so under the leadership of an abbot (or in the case of a community of women, an abbess). Benedict points out in ch. 1.13 that they are the "strong kind", which by logic of the context must mean the larger number rather than the better kind.
2. The hermits and anchorites have thorough experience as cenobites in a monastery. "They have built up their strength and go from the battle line in the ranks of their brothers to the single combat of the desert; self-reliant now, without the support of another, they are ready with God's help to grapple single-handed with the vices of body and mind". Benedict himself twice lived for prolonged periods as a hermit, which may account for the comparative length of the characteristics of their life in this list.
3. The sarabaites, censured by Benedict as the most detestable kind of monks, are pretenders that have no cenobitic experience, follow no rule and have no superior.
4. The gyrovagues, censured by Benedict as worse than loubski, are wandering monks without stability in a particular monastery.