1. a visible sign of an inward grace, esp. one of the solemn Christian rites considered to have been instituted by Jesus Christ to symbolize or confer grace: the sacraments of the Protestant churches are baptism and the Lord's Supper; the sacraments of the Roman Catholic and Greek Orthodox churches are baptism, confirmation, the Eucharist, matrimony, penance, holy orders, and extreme unction. 2. (often initial capital letter ) Also called Holy Sacrament. the Eucharist or Lord's Supper. 3. the consecrated elements of the Eucharist, esp. the bread. 4. something regarded as possessing a sacred character or mysterious significance. 5. a sign, token, or symbol. 6. an oath; solemn pledge.
A sacrament, as defined in Hexam's Concise Dictionary of Religion is what Roman Catholics believe to be "a rite in which God is uniquely active." Augustine of Hippo defined a Christian sacrament as "a visible sign of an invisible reality." The Anglican Book of Common Prayer speaks of them as "an outward and visible sign of an inward and invisible Grace." Examples of sacraments would be Baptism and the Eucharist." Therefore a sacrament is a religious symbol or often a rite which conveys divine grace, blessing, or sanctity upon the believer who participates in it, or a tangible symbol which represents an intangible reality. As defined above, an example would be baptism in water, representing (and conveying) the grace of the gift of the Holy Spirit, the Forgiveness of Sins, and membership into the Church. Anointing with holy anointing oil is another example which is often synonymous with receiving the Holy Spirit and salvation. Another way of looking at Sacraments is that they are an external and physical sign of the conferral of Sanctifying Grace.
Throughout the Christian faith views concerning which rites are sacramental, that is conferring sanctifying grace, and what it means for an external act to be sacramental vary widely. Other religious traditions also have what might be called "sacraments" in a sense, though not necessarily according to the Christian meaning of the term.