Palm Sunday marks the beginning of Holy Week and is an important Christian festival around the world.  It falls on the Sunday before Easter Sunday and is therefore, like Easter, a moveable feast (i.e. a religious celebration or observance which does not occur on the same date each year).  Western Christian churches often refer to Palm Sunday as ‘The Sunday of the Passion’, while Orthodox Christian churches may call the festival ‘The Entry of the Lord into Jerusalem’.

Source: www.calendarpedia.com