Holy Wednesday (also known as Spy Wednesday or Good Wednesday) is the Wednesday that falls into the week of Holy Week leading up to Easter. There are two major events that occur on Holy Wednesday in the Gospels - the anointing of Jesus by a woman named Mary and the plotting of Judas Iscariot to betray Jesus to the Sanhedrin. The day is often referred to as Spy Wednesday because of Judas's actions on this day.
The Anointing
Matthew 26:6-13
6 And when Jesus was in Bethania, in the house of Simon the leper,
7 There came to him a woman having an alabaster box of precious ointment, and poured it on his head as he was at table.
8 And the disciples seeing it, had indignation, saying: To what purpose is this waste?
9 For this might have been sold for much, and given to the poor.
10 And Jesus knowing it, said to them: Why do you trouble this woman? for she hath wrought a good work upon me.
11 For the poor you have always with you: but me you have not always.
12 For she in pouring this ointment upon my body, hath done it for my burial.
13 Amen I say to you, wheresoever this gospel shall be preached in the whole world, that also which she hath done, shall be told for a memory of her.
Matthew 26:14-16
14 Then went one of the twelve, who was called Judas Iscariot, to the chief priests,
15 And said to them: What will you give me, and I will deliver him unto you? But they appointed him thirty pieces of silver.
16 And from thenceforth he sought opportunity to betray him.