What is "Spy Wednesday"?

As the days of Holy Week move forward, various events occur that directly lead to what will take place on Good Friday. Among these events was the fateful betrayal of Jesus by one of his own disciples. 
 
Then one of the twelve, who was called Judas Iscariot, went to the chief priests and said, “What will you give me if I deliver him to you?” And they paid him thirty pieces of silver. And from that moment he sought an opportunity to betray him. (Matthew 26:14-16) 
 
This action by Judas earned him the title of “spy” by medieval Christians, in accord with the traditional definition of the English word, “one who keeps secret watch on a person or thing to obtain information.” 
 
From Wednesday onward, Judas secretly watched for a chance to turn Jesus over to the chief priests, and so many Christians labeled this day as “Spy Wednesday.” 
 
In the same vein various cultures reflected the somber mood of this day by calling it “Black Wednesday” or “Wednesday of Shadows,” which also corresponds to the liturgical rite of Tenebrae that is celebrated on this day. 
 
It is also called “Silent Wednesday,” as the Gospels do not record any activities in the life of Jesus. The only event is the secret meeting of Judas with the chief priests. 
 
Wednesday’s events usher in the final days of Jesus’ life on earth and directly lead to the sacrifice of Jesus on Good Friday.