Panis angelicus is the penultimate strophe of the hymn Sacris solemniis written by Saint Thomas Aquinas for the Feast of Corpus Christi as part of a complete liturgy of the Feast including prayers for the Mass and the Liturgy of the Hours.
The strophe of Sacris solemniis that begins with the words "Panis angelicus" (bread of angels) has often been set to music separately from the rest of the hymn. Most famously, in 1872 César Franck set this strophe for tenor, organ, harp, cello, and double bass; later arranging it for tenor, chorus, and orchestra, he incorporated it into his Messe solennelle Opus 12.
Here is my performance of this famous piece by César Franck.
Ps. The sounds are from GPO4 except the organ.