In Christianity, Holy Monday is the last Monday prior to Easter Sunday; it is the second day of Holy Week after Palm Sunday. Some denominations celebrate Holy Monday, and some do not. The Eastern Orthodox Church observes the day, typically marking it with Bible readings and certain hymns.
According to tradition, Holy Monday is the day on which Jesus cleansed the temple, was praised by local children, and cursed the fig tree (Matthew 21:12–22). It is the day following Palm Sunday, when Jesus came to Jerusalem in the triumphal entry (Matthew 21:1–11). The following day is sometimes referred to as Holy Tuesday, the third day of Holy Week.
We should note that events in the biblical Gospels were not necessarily written in chronological order. Also, since the Romans and the Jews had different methods for calculating the start of a day, an exact sequence of events is difficult to determine. For these reasons, we can’t be dogmatic about the chronology of events leading up to Jesus’ betrayal and crucifixion.
https://www.gotquestions.org/Holy-Monday.html