Holy Monday is the Monday of Holy Week, the week leading to Easter. For the Western Roman Catholic church, Holy Monday is the second day of Holy Week (coming after Palm Sunday) where as the Eastern Church celebrates it as the third day of Holy Week (after Lazarus Saturday and Palm Sunday).
Two major events happened on Holy Monday - the cursing of the fig tree and the overturning of the tables in the Temple court. After these two events, Jesus stayed in Bethany again, most likely in the home of Lazarus, Mary and Martha. And example of these two events can be found in Mark 11:12-25:
12 And the next day when they came out from Bethania, he was hungry.
13 And when he had seen afar off a fig tree having leaves, he came if perhaps he might find any thing on it. And when he was come to it, he found nothing but leaves. For it was not the time for figs.
14 And answering he said to it: May no man hereafter eat fruit of thee any more for ever. And his disciples heard it.
15 And they came to Jerusalem. And when he was entered into the temple, he began to cast out them that sold and bought in the temple, and overthrew the tables of the moneychangers, and the chairs of them that sold doves.
16 And he suffered not that any man should carry a vessel through the temple;
17 And he taught, saying to them: Is it not written, My house shall be called the house of prayer to all nations? But you have made it a den of thieves.
18 Which when the chief priests and the scribes had heard, they sought how they might destroy him. For they feared him, because the whole multitude was in admiration at his doctrine.
19 And when evening was come, he went forth out of the city.
20 And when they passed by in the morning they saw the fig tree dried up from the roots.
21 And Peter remembering, said to him: Rabbi, behold the fig tree, which thou didst curse, is withered away.
22 And Jesus answering, saith to them: Have the faith of God.
23 Amen I say to you, that whosoever shall say to this mountain, Be thou removed and be cast into the sea, and shall not stagger in his heart, but believe, that whatsoever he saith shall be done; it shall be done unto him.
24 Therefore I say unto you, all things, whatsoever you ask when ye pray, believe that you shall receive; and they shall come unto you.
25 And when you shall stand to pray, forgive, if you have aught against any man; that your Father also, who is in heaven, may forgive you your sins.
For Eastern Catholic Churches that follow the Byzantine Rite, Holy Monday is referred to as Great and Holy Monday with the day beginning at Vespers on Palm Sunday night, repeating some of the hymns from the Praises of the All Night Vigil before. At Small Compline a Canon of three Odes is written by Saint Andrew of Crete. The Matins service for Monday through Wednesday is known as the Bridegroom Service.