Exposition and Benediction of the Blessed Sacrament is a devotion in which the Holy Eucharist is placed in a monstrance or ciborium and exposed for adoration. During this time, hymns of praise are sung, such as "O Salutaris Hostia", and prayers are said. The faithful may pray in quiet and foster a deeper relationship with Christ during this period of adoration. The presider places the Luna with the Host into the monstrance on the altar, after which incense is used to bless the Blessed Sacrament. This devotion has been practiced since at least the 17th century, when it was first codified by Pope Clement XII. It is practiced by both Latin and Eastern Catholic churches.
This image by David Eucaristía is in the public domain.