Kosher salt is a type of salt with large, coarse grains. It’s mined from salt deposits. It’s called kosher salt because its large grain size makes it suitable for the koshering process, which involves removing the blood from meat or poultry prior to preparation.
 
Kosher salt  is less refined (the more coarse the less refined) than your normal table salt, and is often used to add that extra crunch to savoury and sometimes some sweet dishes.
 
Because of its wider grains, the coarse salt is more widely used in the culinary industry, using this salt enhances the flavour of the food rather than making the dish salty.
 
It weighs less than table salt and therefore shouldn’t be substituted in a 1-to-1 ratio in recipes.