From the Desert Fathers

Macarius said to Zacharias, 'Tell me, what makes a monk?' He said, 'Isn't it wrong for you to be asking me?' Macarius said to him, 'I am sure I should ask you, Zacharias my son. There is something that urges me to ask you.' Zacharias said to him, 'As far as I can tell, abba, I think anyone who controls himself and makes himself content with just what he needs and no more, is indeed a monk.'