General definition of saint
In general, the term Saint refers to someone who is exceptionally virtuous and holy. It can be applied to both the living and the dead and is an acceptable term in most of the world's popular religions. The Saint is held up by the community as an example of how we all should act, and his or her life story is usually recorded for the edification of future generations.
The process of officially recognizing a person as a saint, practiced by some churches, is called canonization.
The term Saint is derived from the Latin Sanctus meaning “Holy”. This is a direct translation from the Greek word άγιος (agios) also meaning “Holy”. In its original scriptural usage it simply means “Holy” or “Sanctified”. In this form it can be applied to a “Holy” person, a place (αγιον αρος - The Holy Mountain), a thing, such as Scripture itself (αγιογράφικα - Holy Writing), or even God (αγιον Πνεῦμα - The Holy Spirit). But very soon the early Christians began to using the term “Saint” more narrowly to refer to a specific, exemplary individual. (For a lexical explanation, see Liddel & Scott. )
The earliest known occurrence of άγιος as "Saint" seems to be in The Shepherd of Hermas, chapter 5 (or 13, depending on how chapters are counted), verse 2. (I can't verify this--someone with a Greek copy will have to verify it). "The Shepherd" was authored at about the same time as 2 Peter.
Abbreviation for the term Saint is usually “St.” In cases where multiple Saints are referenced SS. is the norm.
Some theologians believe that many people venerated as Saints never actually existed. The polite term for such "Saints" is ahistorical. Sorting out exactly which Saints are ahistorical is difficult, because of the larger difficulty of proving a negative: the absence of independent records of a Saint's existence doesn't prove she or he never existed; indeed there are no specific records of the existence of many people who lived before the 20th century. The Acta Sanctorum (hagiographical work) of the Bollandists forms a major part of the historiography of named Saints.
There are a large number of Christian saints with what appear to be pagan names. Most likely they were pagans who converted to Christianity and subsequently became Saints. However, it is possible that some pre-Christian deities (especially in Rome's area) were accidentally adopted as saints. It is thought that some cults were “Christianized” in a fairly direct manner. The basis for this is usually a similarity of names. For example, it is now commonly asserted that Saint Brigid was based on the Celtic goddess Brigid. The goddess was popular long before Christianity reached Ireland. Another possibility is the melding of the actual life of the Saint with myths related to pre-Christian gods and heroes. There are some striking parallels to the events portrayed in the lives of certain saints and fables such as Androchles and the Lion.
Definition specific to religion
In the Roman Catholic church, the title of Saint - with a capital 'S' - refers to a person who has been formally canonized (officially recognized) by the Church. This takes place sometime after the person’s death and by this definition, never refers to a living person. Formal Canonization is a lengthy process often taking many years, even centuries. The individual is thoroughly investigated by the church and often a number of visions, miracles, or of the holiness and good deeds the person done while on earth in order to be declared a Saint. Also, by this definition there are many people in heaven who are not Saints simply because their lives were not exemplary (though they still went to heaven) and the church does not wish to uphold the individual as an example to be emulated. They are called saints (lowercase 's').
In contrary to popular belief, Saints are not worshiped - this would violate the Commandments - but they are asked for help or to pray for a person. Saints are usually considered to be specific intercessors for specific problems as well. The term Patron Saint usually defines this purpose. Once a person has been declared a Saint, the body of the Saint is considered to be holy. In past centuries, the bones of saints were distributed as holy artifacts. The ring on the finger of Catholic bishops contains the relic of a Saint. In modern times, however, there is a growing trend to show respect for the body of a Saint by leaving it alone and buried.
In the Eastern Orthodox Church a Saint is defined as anyone who is currently in Heaven, whether recognized here on earth, or not. By this definition, Adam and Eve, Moses, the various Prophets, the Angels and Archangels are all given the title of "Saint". While there is a formal service of Glorification in which a Saint is recognized by the entire church, there is no process of investigation. Popularity is often a key to the Church recognizing a Saint. There are numerous small local followings of countless saints that have not reached the popularity to be recognized by the entire church. For the Orthodox, such recognition is unnecessary. It is believed that God reveals his Saints to us, often by miracles or visions. Example: In Orthodox countries it is often the custom to re-use graves after 3 to 5 years because of the limited space. Bones are respectfully washed and placed in an ossuary, often with the persons name written on the skull. Occasionally when a body is exhumed something miraculous occurs to reveal the persons Sainthood. There have been numerous occurrences where the exhumed bones suddenly give off a wonderful fragrance, like flowers; or sometimes the body is incorrupted, just as it was on the day the person died, despite having not been embalmed (traditionally the Orthodox do not embalm the dead) and having been buried for 3 years. The reason relics are considered sacred is because, for the Orthodox, the separation of body and soul is unnatural. Body and soul both comprise the person, and in the end, body and soul will be reunited; therefore, the body of a saint shares in the “Holiness” of the soul of the saint.
Because the Church shows no true distinction between the living and the dead (The Saints are alive in Heaven) the Orthodox treat the saints as if they were still here. They venerate them and ask for their prayers and consider them brothers and sisters in Christ Jesus. Saints are venerated and loved and asked to intercede for our salvation, but it should be clearly understood that they are not Worshiped; their holiness is from God who alone is worthy of Adoration. As Christ says in the Gospels, "Thou shalt worship the Lord thy God, and him only shalt thou serve." (Matt 4:10). The relics of Saints are highly respected, even more so than the Roman Catholics. As a general rule only clergy will touch relics in order to move them or carry them in procession, however, in veneration the faithful will kiss the relic to show love and respect toward the saint. Every altar in every Orthodox church contains relics, usually of martyrs. The Church building interiors are covered with the Icons of saints.
In the Orthodox Church, baptism is the moment one is born again into Christ. The person entering the baptismal font is not the same person that emerges. It is for this reason that the person is given a new name; always the name of a saint. What is proper is that the person no longer goes by his old name because that person is dead, but uses the new name exclusively. It is also common that instead of birthdays, the person celebrates his Saints Day, the day on the Church calendar ascribed to that particular saint.
Christianity in general
In many Protestant churches, the word is used more generally to refer to anyone who is a Christian. This is similar in usage to St. Paul's numerous references. In this sense, anyone who is within the Body of Christ is “Holy” because of their relationship with Jesus. However, high-church Anglicans and Episcopalians use the term "saint" similarly to the manner in which Catholics use it.
Members of The Church of Jesus Christ of Latter-day Saints follow the Protestant tradition described above, referring to themselves as "Latter-day Saints", or simply "Saints". This is usually preferred over the nickname "Mormons".
Although not recognized by Islamic scholars, the veneration of saints and tombs or shrines in Islam is very widespread and includes all geographical areas of the Muslim world, including the conservative Arabian peninsula. Saints are believed to have a power of intercession with God (Allah), and thus the ability to perform miracles and to give power or blessings, known as baraka .
In most Muslim countries there are religious festivities associated with saints, such as Urs festivals in India and Pakistan or the annual Mawlid in Egypt. On these days, the local saint(s) is/are venerated, and blessings are expected. Believers are nevertheless careful to distinguish between the blessings of the prophets (particularly Moses, Jesus and Muhammad) and those of the saints.
Saints are an important component of popular Islam and are associated with Sufism, which includes many of the mystical branches of Islam. Sufism has several orders with precepts ( tariqa ) for students ( murid ) who seek to follow the teachings of a saint. Although saints are acknowledged by many sufis, Sufism distances itself from the more animistic and cultic aspects of the veneration of saints, which includes, as in popular Christianity, all types of religious paraphernalia and popular rituals.
The closest notion in Judaism is the tzaddik (currently points to a disambiguation page), a righteous person. The Talmud says that at any time at least 36 tzaddikim are living among us: they are anonymous, but it is for their sake that the world is not destroyed. The Talmud and the Kabbalah offer various ideas about the nature and role of these 36 tzaddikim. The term can also be used generically to mean any righteous or saintly person.
Saints are also recognized in Hinduism. However, unlike the Roman Catholic Church, no formal process is required to acknowledge a person as a saint.
Tukaram was a great saint who was believed to have performed miracles and was a devotee of Krishna.
The concept of the bodhisattva in some schools of Buddhism is in some respects comparable to that of the Christian saint.
In many of the more obscure religions of the world, a saint is a man or a woman who has a direct personal link or connection with God and who can put a person on the way back to God. Many gurus overtly or covertly claim to be saints, which followers may believe to be true, even if the objective evidence doesn't match a formal definition of a saint.
In the modern religion of Discordianism, sainthood is given very easily. As one of the two cofounders, Kerry Thornley once said "To be a saint you don't need to do anything special, you just need to suffer a lot" Discordians don't really agree on who (or what) are saints, but fictional characters are considered "saintlier" than real people, and insanity always helps. Yossarian from Joseph Heller's Catch-22, Don Quixote, and Bokonon from Kurt Vonnegut's Cat's Cradle all appear on the Principia Discordia's list of saintly folks
Santeria - Voodoo
The veneration of Catholic saints forms the basis of the Cuban Santerķa religion. In Santerķa, saints are syncretised with Yoruban deities, and are equally worshipped in churches (where they appear as saints) and in Santerķa religious festivities, where they appear as deities ( orishas ) however this practice is condemned by the Catholic Church.
Santeria, Haitian Vodoun, Brazilian Umbanda and other similar religions adopted the Roman Catholic Saints, or the images of the saints, as representations of their own spirits/deities or 'Orishas' in Santeria and 'Lwa' in Vodoun. Although there are many similarities between Vodoun and Santeria, they are different in respect to origin and language (Vodou is French, Santeria is Spanish). The adoption of Catholic Saints was fairly common in the religions that were adapted by the slaves in the New World. It can be understood as a more recent example of the adsorbtion of pre-Christian elements into European "Catholicism"—although with Santeria and Vodoun it seems a lot more one-sided. Although different regions of the world where Catholicism is practiced have varying ways practicing their faith.
The Catholic Church has not really condemned the practices of these "religions" or sub-sects (although there were brief local movements against Vodoun by the Church in Haiti). Perhaps the adoption of the Catholic saints is more of a testament to the durability and adaptability of religions like Vodoun. It is remarkable that Vodoun practitioners can consider themselves Catholic and Vodounists at the same time. The Catholic Trinity is made of three personalities whose exact relation is a subtile point of theology and the saints in the Spanish and French Catholic traditions were virtually worshipped too. Perhaps it is more realistic to say that elements of Catholicism were adapted into Vodoun and Santeria.