MIKE MOSS SAYS:        Larry,    There isn't really a single "official" definition of the term. In general, "hard freeze" is used to imply temperatures that are sufficiently cold, for a long enough period, to seriously damage or kill seasonal vegetation. In our area, this usually means temperatures falling into the upper 20s or lower for at least two to three hours. There are some weather service offices that have established specific criteria for a hard freeze watch or warning that may be more intense than the generic definition I just listed - for example, the Mobile AL forecast office lists criteria for its hard freeze warning as temperatures 26 degrees or lower for at least 5 hours. They intend this warning to alert people to the potential for frozen pipes, radiators, livestock and so on, not just damage to sensitive plants.