Quinquagesima Sunday is the Sunday before Lent begins on Ash Wednesday. Sexagesima Sunday is the second Sunday before Lent. Septuagesima Sunday is the third Sunday before Lent. These names for the three Sundays immediately preceding Lent are no longer commonly used in the Christian liturgical calendar except in the traditional Latin Mass of the Roman Catholic Church.
The word quinquagesima means “fiftieth” and refers to the Sunday that is 50 days before Easter if you include Easter Sunday in the count. The word sexagesimal means “sixtieth” and refers to the Sunday that is 56 days before Easter. The word septuagesima means “seventieth” and refers to the Sunday that is 63 days before Easter. Why were Sexagesima Sunday and Septuagesima Sunday given those names when they are not 60 or 70 days before Easter? The most common speculation is that they were given those names in connection to Quinquagesima Sunday, which is 49 or 50 days from Easter, depending on how you count.
What is the purpose of these liturgical Sundays? Some claim that early Christians did not fast on Saturdays or Thursdays during Lent. So, to get a full forty days of fasting in before Easter, they had to begin fasting three Sundays, or seventeen days, before Ash Wednesday. Others use Septuagesima to mark the beginning of the Carnival season.
Whatever the case, Septuagesima Sunday, Sexagesima Sunday, and Quinquagesima Sunday are not mentioned in the Bible. There is no biblical significance to the three Sundays preceding Ash Wednesday and Lent considering the fact that Ash Wednesday and Lent are not mentioned in the Bible. Christians are free to fast on these days, or celebrate on these days, or treat them the same as any other day, based on their own convictions (Romans 14:5-6).