Septuagesima (in full, 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. The earliest date on which Septuagesima Sunday can occur is January 18 (Easter falling on March 22 in a non-leap year) and the latest is February 22 (Easter falling on April 25 in a leap year).
Septuagesima comes from the Latin word for "seventieth" with Sexagesima and Quinquagesima equalling "sixtieth" and "fiftieth" respectively. They are patterned after the Latin word for the season of Lent, Quadragesima, which means "fortieth", as Lent is forty days long excluding Sundays. Because every Sunday recalls the resurrection of Christ, they are considered "little Easters" and not treated as days of penance. Quinquagesima Sunday is indeed the fiftieth day before Easter (counting inclusively), but the numbers indicated by the names "Sexagesima" and "Septuagesima" do not correspond to the interval between these Sundays and Easter.
(... from Wikipedia on 2012-04-17 14:43:33)