Salt, in itself, is always kosher. “Kosher Salt” is really “koshering salt”; salt used to make meat kosher. In order to make meat kosher, it can’t have any blood. One of the ways you make sure there’s no more blood in the meat is a process called melihah. Basically, to do that, you soak the meat in water, then coat it in salt to draw the blood out. Then you wash the salt off the meat. Kosher salt has big flat grains, which makes it dissolve in water slower and makes it easier to draw the blood out.