A Solemnity of the Roman Catholic Church is a principal holy day in the liturgical calendar, usually commemorating an event in the life of Jesus, his mother Mary, or other important saints. The observance begins with the vigil on the evening before the actual date of the feast. The word is taken from the Latin sollemnitas, a term of uncertain origin but possibly derived from sollus (whole) and annus (year), indicating a celebration occurring at yearly intervals. The Church always celebrates each solemnity every year.