The paten is the shallow plate that holds the bread at the Eucharist, and it is the least conspicuous object on the altar precisely because it is defined by its pairing with the chalice.
Made for the cup
The paten is consecrated with the chalice and reserved with it, and in the older forms it is sized to sit over the mouth of the cup, so the two are designed as a set. It holds the bread that is consecrated and, in the traditions that so believe, becomes the body of Christ, and like the chalice its upper surface is of precious metal or gilt for the same reason. It is purified after communion so that no fragment of the consecrated bread is lost, an act of care that expresses the belief attached to what it has held.
Small variations
The Latin paten is a small disc matched to the priest host, while the Eastern churches use a larger footed dish, the diskos, on which the many particles of bread are arranged in a fixed pattern representing Christ, the Virgin and the saints. In some rites a communion-plate is held under the chin of those receiving to catch any fragment. The object is modest, but its consecration and the care of its purification place it among the sacred vessels rather than the furnishings, the necessary counterpart to the cup.