Holy Week is a week celebrated by Christians. The main parts of this week are Palm Sunday, Good Friday and Easter.
Palm Sunday Takes place on the Sunday before Easter. It celebrates Jesus Christ’s Triumphant entry into Jerusalem, people lined the streets shouting “Hosanna” and they laid palm branches and their cloaks on the ground so that Jesus and the donkey he was riding would have a clean path. It was a celebration because it was thought that he would bring an end to the Roman Empire right then and there. (And the Roman Empire did indeed fall…just not at that point in time)
Holy Thursday this is more focused on in the Catholic church. It remembers the night Jesus was betrayed by Judas for 30 pieces of silver.
Good Friday Celebrates Jesus death by Crucifixion on a Roman Cross for the sins of the world. (That includes you and me.) so that we might be with him forever if we so choose.
Easter/Resurrection Sunday After a period of the better part of 3 days Jesus rose from death and ascended into heaven after appearing to various people. He had won the final battle and defeated death, reuniting us with God, if we choose to follow him.