Vow of silence
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A vow of silence is a vow, usually a religious or a spiritual practice taken in a monastic context, to maintain silence. Known as Mauna in Hinduism, Jainism, and Buddhism, the practice is also integral to some Christian traditions.
Religious orders such as the Benedictines have insisted on this as one of the essential rules of their institutes.
In monasteries of many orders there are specific places and times (usually at night) where speaking was more strictly prohibited. These places were termed "Regular Places" (church, refectory, dormitory etc.) and while the times were termed the "Great Silence".  Outside of these places and times were accorded "recreations" allowing some conversation moderated by charity and moderation. Useless and idle words were universally forbidden.  In active orders the members speak according to the needs of their various duties. 
The Cistercian Order alone that admitted no relaxation from the strict rule of silence,[dubious ] and the Reformed Cistercians maintain its severity (Trappists) though other contemplative Orders (Carthusians, Carmelites, Camaldolese etc.) are much more strict on this point than those engaged in active works.  In order to avoid speaking, many orders (Cistercians, Dominicans, Discalced Carmelites etc.) have a certain number of signs, by means of which the religious may have a limited communication with each other for the necessities that are unavoidable. 
Non religious Examples:
Another vow of silence can be made to express a bold statement. This type may be to speak up controversial issues such as child poverty. An example of is The November 30th Vow of Silence for Free The Children in which students in Canada take a 24 hour vow of silence to speak up against poverty and child labour.
There is also the use of a vow of silence done in order to sharpen other senses, whether they be physical or mental, or to discover certain aspects of oneself. 
- Day of Silence
- Meditation, often silent (but sometimes a mantra is involved) & often originally religious
- Minute of Silence
- Moment of Silence
- Remembrance Day
- Silence procedure