The chalice is the cup that holds the wine at the Eucharist, and what distinguishes it from any other vessel is that it is consecrated and reserved.
A consecrated vessel
In Catholic, Orthodox, Anglican and Lutheran practice the chalice is set apart for the Eucharist and used for nothing else, and in the traditions that consecrate it a bishop blesses it with chrism, after which it may be handled only by those permitted to do so. The rule that the interior be of precious metal, or gilt, follows from what it contains, since the wine is held to become the blood of Christ, and the care taken with the cup is a statement about that belief. It is purified after the rite with particular attention so that nothing consecrated is lost.
Form and restriction
The chalice has a bowl, a knop on the stem to steady the grip, and a wide foot, a form settled for practical and reverent handling rather than for ornament, though the great historic examples are among the finest work of the goldsmith. Whether the laity receive from the chalice at all has been a point of division: the medieval Western church withdrew the cup from the laity, and its restoration to them was one of the demands of the Reformation and later of the liturgical reform, so the vessel itself carries a long argument about who may drink from it.