A solemnity in the liturgical year is a feast day of the highest rank celebrating a mystery of faith such as the Trinity, an event in the life of Jesus, the Blessed Virgin Mary, or important saints. The observance begins with the vigil on the evening before the actual date of the feast.
Feast days in the liturgical year are second importance and assigned one date out of the year for each and every canonized saint. The saints are remembered on their individual feast days with special mention, prayers, and possibly a scripture reading.
Next in line are memorials, which are classified as either obligatory or optional. Memorials commemorate a saint or saints. Obligatory memorials must be observed whereas optional memorials do not have to be observed. Only the memorials of those saints who are of “universal significance” are observed by the whole Church and marked in the general liturgical calendar.