A more thorough explanation:

Definition: A feast is a special day or festival that is celebrated in the ecclesiastical calendar. In Roman law, it is used as a date in a legal instrument. In history, it refers to one of the four principal days of the year, which are March 25 (the annunciation of the Virgin Mary), June 24 (the birth of John the Baptist), September 28 (the feast of St. Michael the Archangel), and December 21 (the feast of St. Thomas the Apostle). These four feast days were used as fixed dates for paying rent and setting terms of courts.

Example: In medieval times, people celebrated the feast of St. Michael the Archangel on September 28 by attending church services and having a big feast with their families and friends.

Explanation: This example illustrates how people in history celebrated a feast day, which was an important event in their religious and social lives. The feast of St. Michael the Archangel was one of the four principal days of the year, and people used it as a fixed date for paying rent and setting terms of courts. By attending church services and having a big feast, people showed their devotion to their faith and their community.