This is pure salt and nothing but salt. It can usually be found in the canning supplies section of most stores. This is the salt to be preferred for most food preservation or storage uses. I'm not precisely sure what makes kosher salt different from canning salt. I'm presuming that it must have been processed in a particular manner in accordance with the kosher dietary laws of the Jewish faith because it is used in preparation of kosher foods.
Grain size can vary from manufacturer to manufacturer.
This type of salt comes in about as many different varieties as coffee and from about as many different places around the world. In general, the types sold in grocery stores, natural food markets and gourmet shops have been purified enough to use in food. This type of salt comes in large chunky crystals and is intended primarily for use in home ice cream churns to lower the temperature of the ice filled water in which the churn sits. It's also sometimes used in icing down beer kegs. It is not, however, the same thing as the sea salt found in food stores.