A tabernacle is the fixed, locked box in which, in some Christian churches, the Eucharist

Eucharist

The Eucharist , also called Holy Communion, the Sacrament of the Altar, the Blessed Sacrament, the Lord's Supper, and other names, is a Christian sacrament or ordinance...

 is "reserved" (stored). A less obvious container, set into the wall, is called an aumbry

Aumbry

In the Middle Ages an aumbry was a cabinet in the wall of a Christian church or in the sacristy which was used to store chalices and other vessels, as well as for the reserved sacrament, the consecrated elements from the Eucharist. This latter use was infrequent in pre-Reformation churches,...

.

Within Catholicism, Eastern Orthodoxy and in some congregations of Anglicanism

Anglicanism

Anglicanism is a tradition within Christianity comprising churches with historical connections to the Church of England or similar beliefs, worship and church structures. The word Anglican originates in ecclesia anglicana, a medieval Latin phrase dating to at least 1246 that means the English...

 and Lutheranism

Lutheranism

Lutheranism is a major branch of Western Christianity that identifies with the theology of Martin Luther, a German reformer. Luther's efforts to reform the theology and practice of the church launched the Protestant Reformation...

, a tabernacle is a box-like vessel for the exclusive reservation of the consecrated Eucharist

Eucharist

The Eucharist , also called Holy Communion, the Sacrament of the Altar, the Blessed Sacrament, the Lord's Supper, and other names, is a Christian sacrament or ordinance...

. It is normally made of metal, stone or wood, is lockable and secured to its altar to prevent the consecrated elements within from being removed without authorization.