Kosher salt refers to a salt that is crystallized under pressure
to produce larger flat flakes of salt. It does not have less
sodium per gram than any other salt. However, because of the
crystal shape difference, it would have less sodium per teaspoon
than, say, table salt (much smaller grains - thus more densely
packed). Weight to weight it would be the same. Kosher salt is
pure sodium chloride and does not have iodine added to it. Sea
salt, as it sounds, is made from dehydrating sea water. Because
it is not crystalized pure it contains many other minerals and
potential nutrients from the sea water. Sea salts from different
parts of the world will have different mineral contents. Sea
salts can add different depths of flavor besides just the
saltiness. "Men never commit evil so fully and joyfully as when
they do it for religious convictions."