The Synaxis of the Glorious and All-Praiseworthy Twelve Apostles of Christ appears to be an ancient Feast. The Church honors each of the Twelve Apostles on separate dates during the year, and has established a general commemoration for all of them on the day after the commemoration of the Glorious and First-Ranked among the Apostles Peter and Paul.
The holy, glorious, all-laudable Apostle Jude is also commemorated on June 19. He is also known as Thaddeus (but should not be confused with St Thaddeus of the Seventy, who is commemorated on August 21), and was the brother of St James (October 23).
For lists of the Apostles’ names, see: Mt.10:2, Mark 3:14, Luke 6:12, Acts 1:13, 26.