Kosher salt is for koshering meat (the complete removal of all traces of blood). Kosher salt is more course than table salt and does not contain iodine. It is more like flakes rather than grains. This property makes it more efficient at koshering than table salt because the flakes can absorb more liquid and it can leave a nice crust on the outside of the meat when dry coated. Many brine recipes call for kosher salt because it is so good at drawing out blood. Brining works through osmosis, as the salt is drawing the blood out the water and seasonings are being forced in. You can get by with using pickling salt in place of Kosher for a brine but I wouldn't substitute with sea salt or table salt.