Coarse-crystalled salt without iodine, favoured in professional kitchens because the large flakes are easy to pinch and see.
What it does in a recipe: Controllable seasoning — the crystal size is the whole point. Pick the swap that covers that job — the ratios below are written so you can act on them without doing any arithmetic.
Diamond Crystal and Morton kosher salt differ from each other by nearly a factor of two by volume. If a recipe specifies a brand, it is not being fussy.
Cooking around an allergy? Diet tags here describe the ingredient itself, not any particular brand. Processed products change formulation without notice and shared production lines are common, so read the label on everything you use. A severe allergy is a medical matter — confirm with the manufacturer or your clinician rather than relying on a substitution chart.