In every Catholic Church, there is a 'box' called the tabernacle where consecrated Hosts (Our Lord Himself) are reserved for adoration, worship, and for distribution of Holy   Communion during the Mass and for the sick. One way to recognize the tabernacle is that usually a red or white candle will be burning very close to it to tell us that our Lord is present in the tabernacle. If the Blessed Sacrament is for some reason removed from the tabernacle, the light will be put out.