A saint is a person who has been recognized by the Catholic Church or the Orthodox Church as doing great works or making a great personal sacrifice for the Christian church. Saints, especially early saints in Christian history, were often martyrs. Many saints are often associated with miracles, either in this life, or, in the Catholic tradition, through miracles that occur when praying to them after death.
In Catholic and Orthodox doctrine, saints are believed to be able to intercede on behalf of mankind before God.
Persons recognized as saints must first be beatified (After which the deceased person is given the title 'Blessed') and then canonized by the Pope. Usually a person is canonized if at least three miracles have been performed by them through lay people asking the deceased to intercede with God on their behalf. These miracles must be thoroughly investigated by church authorities and declared valid before canonization occurs.
Many martyrs, people who died either for their faith or for another person, are recognized as saints based upon what Jesus said; the greatest commandments are to love God with your whole heart and soul and to love your neighbor as yourself. Also, when he told His disciples that 'greater love than this no man hath, that a man lay down his life for his friends.'
The Queen of Saints is Mary, the Mother of Jesus the savior, also known as the Blessed Virgin. The feast of All Saints is November 1st preceded by All Hallow's Eve which refers to All Saints Day.
Beatification and Canonization, http://www.newadvent.org/cathen/02364b.htm