One of the first questions people ask about a certain palm is its cold hardiness or cold tolerance (both mean the same thing).  This refers to the minimum temperature that a palm can withstand before it begins to freeze to death.  Different types of palms come from different parts of the world.  Some come from tropical rainforests while some come from hot, dry deserts.  A palm’s natural habitat is where it has been growing since the beginning of time (in most cases).  Thus, the palm has become accustomed to the climate, conditions, and environment around it.  If a palm is subjected to colder or drier conditions than it is used to in its native home, it can suffer damage or even death. 
Simply put, a palm has a temperature and humidity range in which it is able to photosynthesize and grow.  If the temperature falls below this range, the cells in the palm’s leaves (chlorophyll) stop photosynthesizing and begin to die.  The leaves will be the first to go, followed by the stems, crown, and lastly the main trunk.  Some palms have been chilled long enough to lose all their leaves (defoliate) but not long enough to freeze the grow point (crown).  In this case, the palm will usually recover by pushing new growth once temps become warmer.  Full recovery can take years.