Why do we often call the Sunday before Easter Palm Sunday?
Palm Sunday is the day we celebrate Jesus' triumphal entry into Jerusalem the week before His resurrection from the dead. Jesus had just raised Lazarus from the dead and had become somewhat of a celebrity among the Jewish people. He came into town riding on a colt, the foal of a donkey. A large crowd lined the streets when people heard that he was coming. They cut off palm branches, took off their cloaks to place on the ground before Him, and waved palm branches in the air while crying, "Hosanna to the Son of David! Blessed is he who comes in the name of the Lord! Hosanna in the highest heaven!" Matthew 21:9
This all happened in fulfillment of a Messianic prophecy in Zechariah 9:9, and the crowds were quoting a Messianic Psalm Psalm 118:25-26.