They etymology of the word sacrament shows that it came from the Latin sacramentum "a consecrating", from sacrare "to consecrate". It was a Church Latin loan translation from the Greek word mysterion which meant "mystery".
Working definitions vary considerably among different Christians. Most Protestants believe that sacraments are an "outward sign of an inward grace", or that they are "only symbols" of what is taking place or has taken place invisibly. They most often practice two sacraments: baptism and communion. Many Anabaptist churches practice foot washing, citing the commandment of Jesus Christ in John 13:14: "If I then, your Lord and Master, have washed your feet; ye also ought to wash one another's feet." Other Protestant Churches may practice more or fewer sacraments.
Catholicism and Eastern Orthodoxy teach that the sacrament itself is an effective means of grace, and is not "just a symbol". They traditionally practice seven sacraments but also acknowledge that there can be additional means of grace as well; see Catholic sacraments.
In Eastern Orthodoxy the use of sacraments is an affirmation of the goodness of created matter, and many times an emphatic declaration of what that matter was originally created to be. They often call the sacraments "mysteries", as in the "Mystery of Repentance". They have many such sacraments, some more emphasized than others, and traditionally have not systematically enumerated them. The central sacrament is of course the Eucharist.
Quakers practice no formal sacraments, believing that all activities can and should be considered holy. The Salvation Army also does not practice any formal sacraments for a variety of reasons; it also does not forbid its members from receiving sacraments in other denominations .
See also: Sacrament (Mormonism)