Kosher salt is a course-grained natural salt with no additives. It is used for creating kosher meat by salting the meat to remove excess blood after animal slaughter.
The name is a bit misleading. It would more accurately be called "salt for making meat kosher." For use in eating, all salt is kosher, that is acceptable to eat.
People like kosher salt for the same reason that they like course-ground sea salt. Kosher salt has large grains that give a different flavor. It's really nice sprinkled on kabobs on the grill.