Clean Monday (Greek: Καθαρά Δευτέρα), also known as Pure Monday, Ash Monday, Monday of Lent or Green Monday, is the first day of Great Lent throughout Eastern Christianity and is a moveable feast, falling on the 7th Monday before Easter (Greek : Πάσχα). This year (2021) it it celebrated on March 15th.
Clean Monday – and thus Lent itself – begins on the preceding (Sunday) evening, at a special service called Forgiveness Vespers, which culminates in the Ceremony of Mutual Forgiveness, where all present will bow to one another and ask forgiveness. In this way, the faithful begin Lent with a clear conscience, with forgiveness and with renewed Christian love. The entire first week of Great Lent is often called “Clean Week,” and it is customary during this week to go to confession and thoroughly clean the house.
Clean Monday is an official holiday in Greece, where it is celebrated with outdoor excursions, the consumption of shellfish and other solid foods, a special kind of bread, baked only on that day, called “lagana” (Greek: λαγάνα) and the widespread custom of kite flying.
In this way, the Orthodox celebrate the fact that “the spring of fasting has arrived, the flower of repentance begins to open”