Palm Sunday is a moveable feast in the church calendar observed by Catholic, Orthodox, and some Protestant Christians. It is the Sunday before Easter Sunday, and a celebration of the entry of Jesus into Jerusalem in the days before his execution. The crowd greeted him by waving palm fronds, giving the day its name.
In the Roman Catholic Church, it is now often referred to as Passion Sunday, and is the beginning of Passion Week (formerly called "Holy Week" officially, and still usually referred to as such by the general public). In the Passion Week liturgy on Palm Sunday palm fronds are blessed outside the church building and a procession enters, singing, re-enacting the entry into Jerusalem. In the Western church it must always fall on one of the 35 dates between March 15 and April 18
In the Eastern Orthodox Church, it is often called the Entry into Jerusalem, and is the beginning of Holy Week. The day before it is Lazarus Saturday, remembering the resurrection of Lazarus from the dead. On Lazarus Saturday believers often prepare palm fronds by knotting them into crosses in preparation for the procession on Sunday. In the Russian Orthodox Church, the custom developed of using pussy willows instead of palm fronds because palm fronds were not readily available.