Kosher Salt or Koshering Salt
I'm Jewish. I'm religious. But I buy regular salt in the supermarket like everybody else does. As long as you ensure there's no additives, salt is salt is salt.
What may be being referred to is Salt for the purpose of Koshering meat. One of the laws of Kashrut (the Jewish dietary laws) specifies that we can't eat any blood, and therefore it has to be drained from the body of the animal. This is why reason for the method of ritual slaughter, with a swift cut through the neck (shechitah).
Following on from this, the meat is then salted to draw out the blood. And this is where koshering salt comes into the game. As mentioned, it's coarse and doesn't clump, and is therefore easy to spread all over the meat. It's then left on the meat for a while (I can't remember how long), and rinsed off.