When the bishop or priest repeats the words of consecration during the Mass, the bread and wine become the Body and Blood of Christ. Only the appearance of bread and wine remain. This mystery of Faith is known as the "Real Presence" of Christ in the Eucharist. "This presence is called 'real' not to exclude the idea that the others are 'real' too, but rather to indicate presence par excellence, because it is substantial and through it Christ becomes present whole and entire, God and man" (Bl. Paul VI, MF 39; cf. Council of Trent, Decree on the Holy Eucharist, c. 3). (Cf. CCC 1377)

It became the custom in the early Church to set aside some consecrated hosts when the Mass had ended; today, every Catholic church has a tabernacle where the Body of Christ is reserved. The Eucharist is thereby available to distribute to the sick who could not attend Mass.

Since Christ is truly present, an act of reverence is made toward the tabernacle; in the Western Church a genuflection, by which the rigit knee is touched to the ground, is normally used.

The Real Presence of Christ invites us also to the adoration of the reserved Blessed Sacrament; this has led to the development of many Eucharistic devotions. Eucharistic adoration before the tabernacle is one such pious practice. 

Many churches also have periods of adoration when a consecrated host is displayed, or exposed, in a monstrance. Some churches have chapels for perpetual adoration, which is prayer before a host that is exposed continuously. The Forty Hours devotion is practiced in many churches that do not have perpetual adoration.

Eucharistic processions are conducted when the Eucharist is placed in a monstrance, which is then carried around church and even through the streets of the town or city. (Cf. CCC 1378-1379)



The Catechism of the Catholic Church addresses this question in paragraphs 1378-1379

-The Didache Bible