A friar is a religious who is a member of one of the four mendicant or "begging" orders which includes the Dominicans, Franciscans Carmelites and Augustinians. Unlike a monk, a friar is not cloistered and can be sent into public ministry in varying capacities, from missionary work to be a local confessor.
The Cistercians or Trappists are quite strict in their dedication to the cloistered monastic lifestyle.
cloistered:
No, Luke founded no religious orders.
All Religious should have contemplation as the core of their spiritual life. However, technically speaking, an apostolic religious is one who is not cloistered* and who has an additional ministry among the people of God. A contemplative is usually a cloistered religious whose way of life allows more time for meditation and contemplation, and whose day, (in the Catholic Church) is woven around the "Hours", which are prayers said together at certain times throughout the day.. *A cloistered religious lives in a monastery and usually remains there. Visitors are strictly regulated. The Catholic Church has rules and regulations regarding cloister. This is, at least, how I understand the terms.
In 2013 there were 12,350 religious priests (in other words priests in religious orders as opposed to diocesan priests), all of whom may offer Mass, and there were 4,407 brothers in religious orders; for a total of 16,757 men in religious orders.
All nuns started out as cloistered, that is the very definition of a nun, as opposed to a Sister. A Sister works out in the world, classically, teaching, nursing, etc. Nuns, such as Benedictines, Cistercians, Carthusians, were all cloistered, although many, not all, modern Benedictine nuns work out in the world like Sisters. (Cloistered is the term for an "enclosed Order". Classically, Carmelites, Visitation Sisters, Franciscans, Dominicans, and many others were cloistered as well, but they are not nuns.
By sister you mean religious sisters then a nun is cloistered (sequestered) and a sister leads a life of service.
Each order has its own rules and regulations and suggestions when it comes to entry into the order. Your best bet is to contact the order directly. Cloistered orders take a vow of poverty and members are allowed few, if any, personal possessions.
The Ursulines are Sisters not nuns. They were founded in the sixteenth century and were the very first Order that was founded that was not composed of cloistered nuns, instead they were founded for the education of young girls so the Sisters were not to be cloistered but to be out in the community. There was Episcopal opposition to a religious order of women that was not strictly cloistered, at that time.
Cloistered = a verb in the Past Participle.
"Cloistered" in the given sentence is a verb, part of the past tense in the passive voice of the verb "cloister". The complete verb is "were cloistered".