Palm trees are evergreens so, like other evergreens, are symbolic of eternity, long life, and the eternal life of the spirit.  The palm is also a solar symbol as it grows mostly in tropical, sunny areas and was the emblem of Apollo.  Also, looking up at a palm tree from the base, it is shaped liked the sun with the fronds like rays of sunlight.   Palms can also symbolize triumph such as when palms were thrown in front of Jesus as he rode into Jerusalem.  Plutarch said the palm represented victory.  Palm represents victory over death and sin.  Palms were often displayed in early Christian funerals to symbolize the persons passage into immortal life in spirit.  Eagles and Phoenix are sometimes depicted holding palm fronds thereby doubling the symbology of eternal life or rebirth.  It can also represent the Tree of Life.  In Judaism, palms represent peace and plenty.  Palm also represent hospitality is parts of the world and it is claimed the the prophet Muhammad built his house of palm.  The ancient Assyrians used palm as a symbol of Ishtar , another solar god (or goddess in this case).