I thought it would be wise to post some basics of our faith for my non-Catholic readers.
A saint is simply a person that, by living a life of faith and virtue, is now in Heaven. These special people are wonderful intercessors between God. Because of their closeness with God, these men and women can pray for else.
The term "saint" originated for Latin sanctus meaning "hallowed or consecrated." The first person honored individually as a saint was the first martyr, Stephen. For nearly 4 centuries, prayer to St. Stephen for his intercession and prayers was popular. Beginning at the end of the Second Century, special celebrations were created annually on the anniversaries of the martyrs' deaths. These martyrs (those that die because they refuse to renounce Jesus Christ) were witnesses of Christ and were certainly in Heaven. Even Jesus says in Matthew Chapter Five that whoever is persecuted for Him would be rewarded in Heaven.
By 327 Christianity was finally legalized and sainthood was not just considered for martyrs but for ascetics, confessors, and virgins. Saints could be monks, nuns, teachers, bishops, or any average citizen. This is why we know there are many, many more saints than we know of. This is the point of All Saints Day - honor all saints, known and unknown.
Note: When I use the word "cult" it is used in its technical sense rather than with the negative connotations of today.
During the papacy of Innocent III (1199 - 1216), all new cults required papal approval. This finally formed the structured process of canonization in 1634. Beatification, the step before sainthood where 1 after death miracle is required, became introduced at this time.
Today, to be considered a saint, one must have performed two after-death miracles. These usually involve miraculous cures that modern medicine cannot prove. Beatification requires only 1 of these miracles. In addition, an intense examination of the person's writings and interviews about their entire life are conducted. Prior to Vatican II, beatification required two miracles and canonization required three.