...Got this from Google..."Palm Sunday falls on the Sunday before Easter. The feast commemorates Jesus' triumphal entry into Jerusalem, an event mentioned in all four canonical Gospels".
....."according to the Gospels, Jesus rode a donkey into Jerusalem, and the celebrating people there lay down their cloaks in front of him, and also lay down small branches of trees.
......"John more specifically mentions palm fronds. The palm branch was a symbol of triumph and victory in Jewish tradition, and is treated in other parts of the Bible as such"