A paten, or diskos, is a small plate, usually made of silver or gold, used to hold Eucharisticbread which is to be consecrated. It is generally used during the service itself, while the reserved hosts are stored in the Tabernacle in a ciborium.
Western Usage
Within the Latin-Rite, the paten is typically either a simple saucer-like plate or a low bowl. A smaller style paten will often have a depression that allows it to securely sit on top of the chalice.
In more traditional denominations or parishes, altar servers may also use a small paten, usually attached to a short pole, which is placed under the chin of those receiving the Eucharist on the tongue; thus if the host accidentally falls, it would land on the paten rather than the floor.
The General Instruction of the Roman Missal lays down rules for patens: <blockquote>"...should be made from solid materials which are considered suitable in each region. The conference of bishops will be the judge in this matter. Materials which do not break or deteriorate easily are to be given preference."