(1) A monastery becomes an abbey much as a child grows, develops and becomes an adult. There is a fundamental difference between a monastery and an abbey. A monastery is a building where people live the monastic life. An abbey is a religious community of monks that has an abba, or father, as its leader. An abbey can also be a religious community of women whose leader is an abbess.
(2) Basically, an abbey must have at least a dozen religious whereas a monastery doesn't. An abbey is usually built around a walled-in quadrangle that contains a novitiate, a guest house, choir, oratory for prayer, infirmary, conference room, kitchen, refectory or dining room, cells for the religious or dormitory, cellars for storage, a small parlor, a revolving door or almonry for alms and gifts, food, etc. from outsiders, and a chapter house for private meetings with the abbot for men or abbess for women. Benedictine and Cistercian Orders have abbeys, while most other contemplative, cloistered orders call them monasteries. Finally, an abbey is like a diocese since the abbot enjoys the same powers as the bishop save the Apostolic succession. In fact, the abbot has independent power over the abbey which a bishop has no authority over because an abbey is usually a territorial jurisdiction. The word "abbey" means "House of the Father" who is the abbot, a word derived from the Aramaic abba meaning "Father."
(3) An abbey is an independent monastery with a required minimum of members of religious orders, led by an abbot or abbess. Most abbeys are either Benedictine or Carthusian.
Benedict of Nursia founded the first abbey at Monte Cassino near Rome in the sixth century. By 1415, there were over fifteen thousand abbeys following his rule. Abbeys were usually established on arable land because they were intended to be self-sufficient centers of prayer, productivity, and communal harmony.
Abbeys were also centers of culture, learning, and social progress. Monks established schools, copied and illuminated manuscripts, improved farming methods, and organized early cooperative farming. They developed the first hospitals in the West because of their care of the sick on pilgrimage.
A monastery (Gk., monos, “alone”; “hermit’s cell” or “group of protected cells”), is the dwelling place of monks, clerics living a communal life, or nuns. In the West, the term is generally reserved for Benedictine houses or houses derived from the Rule of St. Benedict. Defining characteristics of a monastery are separation from the world; the monk’s permanent attachment to the place of profession; virtual autonomy of government of the individual house; and commitment of members to a classical monastic rule. Historically the entire Liturgy of the Hours is celebrated in common.