Septuagesima Sunday is the name for the ninth Sunday before Easter, the third before Ash Wednesday. The term is sometimes applied also to the period that begins on this day and ends on Shrove Tuesday, the day before Ash Wednesday, when Lent begins. This period is also known as the pre-Lenten season or Shrovetide. The other two Sundays in this period of the liturgical year are called Sexagesima and Quinquagesima, the latter sometimes also called Shrove Sunday.
Septuagesima comes from the Latin word for "seventieth." Likewise, Sexagesima, Quinquagesima, and Quadragesima mean "sixtieth," "fiftieth," and "fortieth" respectively. Septuagesima Sunday is so called because it falls within seventy days but more than sixty days before Easter. The next Sunday is within sixty, Sexagesima, and the next within fifty, Quinquagesima. Falling within forty days of Easter (excluding Sundays) the next Sunday is Quadragesima, the Latin word for the season of Lent, which (not counting Sundays) is forty days long. Because every Sunday recalls the resurrection of Christ, they are considered "little Easters" and not treated as days of penance.
The 17-day period beginning on Septuagesima Sunday is intended to be observed as a preparation for the season of Lent, which is itself a period of spiritual preparation for Easter. The “Alleluia” ceases to be said during the liturgy, and the Gloria in excelsis is not used. Likewise, violet vestments are worn, except on feasts, from Septuagesima Sunday until Holy Thursday.