As defined by the Catechism of the Catholic Church, the Liturgical Year is "The celebration throughout the year of the mysteries of the Lord's birth, life, death, and Resurrection in such a way that the entire year becomes a 'year of the Lord's grace'.
Thus the cycle of the liturgical year and the great feasts constitute the basic rhythm of the Christian's life of prayer, with its focal point at Easter.
The Liturgical calendar follows three year cycles:
In year A Matthew is the primary gospel.
In year B Mark is the primary gospel.
In year C Luke is the primary gospel.
Following is an alphabetical list of the principal feasts and liturgical seasons from the Catechism:
Advent - The liturgical season of four weeks devoted to preparation for the coming of Christ at Christmas (524).
Annunciation - The visit of the angel Gabriel to the virgin Mary to inform her that she was to be the mother of the Savior. After giving her consent to God's word, Mary became the mother of Jesus by the power of the Holy Spirit (484, 494).
Ascension - The entry of Jesus' humanity into divine glory in God's heavenly domain, forty days after His Resurrection (659,665).
Assumption - The dogma that recognizes the Blessed Virgin Mary's singular participation in her Son's Resurrection by which she was taken up body and soul into heavenly glory, when the course of her earthly life was finished (2124-5).
Christmas - The feast of the Nativity, the birth of Jesus (1171).
Easter - The greatest and oldest Christian feast, which celebrates Christ's Resurrection from the dead. Easter is the "feast of feasts", the solemnity of solemnities, the "Great Sunday". Christians prepare for it during Lent and Holy Week, and catechumens usually receive the Sacraments of Christian Initiation (Baptism, Confirmation, Eucharist) at the Easter Vigil (1169; cf. 647).
Epiphany - The feast that celebrates the manifestation to the world of the newborn Christ as Messiah, Son of God, and Savior of the world. The feast of Epiphany celebrates the adoration of Jesus by the wise men (magi) from the east, together with his baptism in the Jordan and the wedding feast of Cana in Galilee (528; cf. 535).
Feast Days - The annual cycle of liturgical celebrations commemorating the saving mysteries of Christ's life, as a participation in the Paschal Mystery, which is celebrated annually at Easter, the "feast of feasts." Feast days commemorating Mary, the Mother of God, and the saints are also celebrated, providing the faithful with examples of those who have been glorified with Christ (1169, 1173).
Holy Days of Obligation - Principal feast days on which, in addition to Sundays, Catholics are obligated by Church law to participate in the Eucharist; a precept of the Church (2043, 2180).
Holy Week - The week preceding Easter, beginning with Palm (Passion) Sunday, called the "Great Week" in the liturgies of the Eastern Churches. It marks the Church's annual celebration of the events of Christ's passion, death, and resurrection, culminating in the Paschal Mystery (1169).
Immaculate Conception - The dogma proclaimed in Christian Tradition and defined in 1854, that from the first moment of her conception, Mary -- by the singular grace of God and by virtue of the merits of Jesus Christ -- was preserved immune from original sin (491).
Pentecost - The "fiftieth" day at the end of the seven weeks following Passover (Easter in the Christian dispensation). At the first Pentecost after the Resurrection and Ascension of Jesus, the Holy Spirit was manifested, given and communicated as a divine Person to the Church, fulfilling the paschal mystery of Christ according to His promise (726, 731; cf.1287). Annually the Church celebrates the memory of the Pentecost event as the beginning of the new "age of the Church", when Christ lives and acts in and with His Church (1076)