七旬斋是西方基督教会大斋节前的第三个星期日，复活节前的第70天（拉丁文septuagesimus意为「第七十」）。七旬斋之名显然是由「四旬斋」（Quadragesima）和「五旬斋」（Quadragesima）类推而得。

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 commonly called Shrovetide (the Pre-Lenten Season) that begins on this day and ends on Shrove Tuesday, the day before Ash Wednesday, when Lent begins.