Moveable feast

In Christianity, a moveable feast or movable feast is an observance in a liturgical calendar that occurs on different dates (relative to the dominant civil or solar calendar) in different years. The most important set of moveable feasts are a fixed number of days before or after Easter Sunday, which varies by over 40 days since it depends partly on the phase of the moon. In Eastern Christianity, these moveable feasts form what is called the Paschal cycle.