Viaticum is a term used especially in the Roman Catholic Church

Roman Catholic Church

The Catholic Church, also known as the Roman Catholic Church, is the world's largest Christian church, with over a billion members. Led by the Pope, it defines its mission as spreading the gospel of Jesus Christ, administering the sacraments and exercising charity...

 for the Eucharist

Eucharist

The Eucharist , also called Holy Communion, the Sacrament of the Altar, the Blessed Sacrament, the Lord's Supper, and other names, is a Christian sacrament or ordinance...

 (communion) administered, with or without anointing of the sick

Anointing of the Sick

Anointing of the Sick, known also by other names, is distinguished from other forms of religious anointing or "unction" in that it is intended, as its name indicates, for the benefit of a sick person...

, to a person who is dying, and is thus a part of the last rites

Last Rites

The Last Rites are the very last prayers and ministrations given to many Christians before death. The last rites go by various names and include different practices in different Christian traditions...

. According to Cardinal

Cardinal (Catholicism)

A cardinal is a senior ecclesiastical official, usually an ordained bishop, and ecclesiastical prince of the Catholic Church. They are collectively known as the College of Cardinals, which as a body elects a new pope. The duties of the cardinals include attending the meetings of the College and...

 Javier Lozano Barragán, "The Catholic tradition of giving the Eucharist to the dying ensures that instead of dying alone they die with Christ who promises them eternal life

Eternal life (Christianity)

In Christianity the term eternal life traditionally refers to continued life after death, rather than immortality. While scholars such as John H. Leith assert that...

." For Communion as Viaticum, the Eucharist is given in the usual form, with the added words "May the Lord Jesus Christ protect you and lead you to eternal life".
The word viaticum is a Latin word meaning "provisions for a journey," from via, or "way." The Eucharist is seen as the ideal food to strengthen a dying person for the journey from this world to life after death.

The desire to have the bread and wine consecrated in the Eucharist available for the sick and dying led to the reservation of the Blessed Sacrament

Blessed Sacrament

The Blessed Sacrament, or the Body and Blood of Christ, is a devotional name used in the Roman Catholic Church, Eastern Catholic Churches, Old Catholic, Anglican, and Lutheran churches, to refer to the Host after it has been consecrated in the sacrament of the Eucharist...

, a practice which has endured from the earliest days of the Christian Church. Saint Justin Martyr

Justin Martyr

Justin Martyr, also known as just Saint Justin , was an early Christian apologist. Most of his works are lost, but two apologies and a dialogue survive. He is considered a saint by the Roman Catholic Church and the Eastern Orthodox Church....

, writing less than fifty years after the death of Saint John the Apostle

John the Apostle

John the Apostle, John the Apostle, John the Apostle, (Aramaic Yoħanna, (c. 6 - c. 100) was one of the Twelve Apostles of Jesus. He was the son of Zebedee and Salome, and brother of James, another of the Twelve Apostles...

, mentions that “the deacons communicate each of those present, and carry away to the absent the consecrated Bread, and wine and water.” (Just. M. Apol. I. cap. lxv.)

If the dying person cannot take solid food, the Eucharist may be administered in the "species" (appearance) of wine alone, since the bread and wine are the Body, Blood, Soul and Divinity of Christ.

The sacrament of Anointing of the Sick is often administered immediately before giving Viaticum if a priest

Priest

A priest is a person authorized to perform the sacred rites of a religion, especially as a mediatory agent between humans and deities. They also have the authority or power to administer religious rites; in particular, rites of sacrifice to, and propitiation of, a deity or deities...

 is available to do so. Unlike the Anointing of the Sick, Viaticum may be administered by a priest, deacon

Deacon

Deacon is a ministry in the Christian Church that is generally associated with service of some kind, but which varies among theological and denominational traditions...

 or extraordinarily (and only in special circumstances) by a lay minister, using the reserved Blessed Sacrament.

Alternatively, viaticum can refer to an ancient Roman provision or allowance for traveling, originally of transportation and supplies, later of money, made to officials on public missions; mostly simply, the word indicates money or necessities for any journey. Contrary to church doctrine, during late Antiquity

Late Antiquity

Late Antiquity is a periodization used by historians to describe the time of transition from Classical Antiquity to the Middle Ages, in both mainland Europe and the Mediterranean world. Precise boundaries for the period are a matter of debate, but noted historian of the period Peter Brown proposed...

 and the early medieval period the host was sometimes placed in the mouth of a person already dead, perhaps owing to traditional superstition that scholars have compared to the pre-Christian custom of Charon's obol

Charon's obol

Charon's obol is an allusive term for the coin placed in or on the mouth of a dead person before burial. According to Greek and Latin literary sources, the coin was a payment or bribe for the ferryman who conveyed souls across the river that divided the world of the living from the world of the dead...

, a small coin placed in the mouth of the dead for passage to the afterlife and sometimes called a viaticum in Latin literary sources.