The second multi-day fast dedicated to the Holy Apostles has begun, which begins after All Saints' Sunday and lasts until July 12.
Since it ends the day before Peter's Day, it is called the Peter's Fast. This fast, whose beginning is movable (because it depends on the Feast of Feasts), and whose end is immovable, was established based on the memory of the apostles who, after the Descent of the Holy Spirit, and before leaving to preach the Seventh Gospel, fasted (Acts 13:2-3). Due to the dependence of the beginning of this fast on Easter, the Apostolic Fast can last at least one week and one day, and at most six weeks.

Fasting as an integral part of liturgical life

George S. Deboljski: Days of Divine Service (Book of Fasting) of the Orthodox Catholic Eastern Church (Apostolic Fast)...

https://svetigora.com/apostolistski-petrovski-post/